These fun rhubarb and custard blondies will keep you coming back for more! Delicious, buttery squares topped with rhubarb compote, custard and white chocolate drizzle.
They are soft and gooey in the middle, with crispy and chewy edges. Perfect treat to share with your friends and family! The recipe comes together super quick and you don't even need any special equipment to make them!
Why you will love this recipe
Firstly, the combination of rhubarb and custard is simply delicious. Different flavours and contrasting textures of these two are a true excitement for the taste buds. Tart and tender rhubarb plus sweet, velvety- smooth custard are just perfect together. There has been many combinations of these two ingredients in desserts over the years, but this one, by far, is my favourite.
These dense, fudgy and gooey little squares are just perfect for whenever you need a quick fix of something sweet, but don't fancy baking a cake or anything too complicated.
Key ingredients and substitutions
These rhubarb and custard blondies are made using pantry staples, and most of them are more likely in your kitchen cupboard already. Let's have a look at some of the key ingredients:
Rhubarb - I like to use fresh rhubarb, but frozen or canned rhubarb will also work. If you are using canned rhubarb, make sure to drain it first. Whichever type of rhubarb you decide to use, it almost always needs some sugar added to it, to reduce its tartness. You may not need the whole amount that the recipe calls for, but any leftovers can be stored in the fridge and used to top up your porridge, yogurt or pancakes.
Custard - The recipe calls for two types of custard: powdered and ready-made. Powdered custard is used in the cake batter, to replace part of flour and create that delicious, buttery taste. Ready-made custard is used on top, along with rhubarb. But you can use only powdered custard in the whole recipe. See the recipe notes for instructions.
White chocolate - You will need about 200 g of white chocolate in total. I normally use bar of chocolate and chop it into small chunks. That said, you can use chocolate buttons, chips or wafers.
Sugar - There are two different types of sugar in this recipe, caster (or regular white) and soft light brown sugar. Technically, you can stick just to caster / granulated white sugar, but I like to mix both types into the batter. Brown sugar adds that delicious, mellow, almost caramel-like taste to bakes and helps to keep the texture of blondies nice and soft.
Eggs - I have tested this recipe with 3 medium eggs, or two large eggs, and in both cases, it worked fine. Feel free to use whichever type you have available.
How to make these blondies
If you would like, watch this Instagram Reel to see how easy it is to make these blondies!
Start by prepping your rhubarb and custard topping. If you are using fresh rhubarb, cut it into smaller chunks (roughly about 2- 3 cm long) and place it in a wide saucepan with caster sugar and 2 tablespoon of water. Cook it until it starts to break up and becomes jammy. If you'd like, you can add few drops of pink food colouring to intensify the colour of the compote.
If you are using powdered custard only in this recipe, prepare the custard topping at this stage. You will need about 5 tablespoon of custard for the topping in total.
Alternatively, if you don't fancy cooking and stewing the rhubarb first, you may want to check out the recipe for Rhubarb and White Chocolate Blondies from Hummingbird High ,where whole chunks of rhubarb are used on top.
To make blondies batter, start by melting butter and both sugars together until you have thick mixture that is smooth and glossy. Allow the mixture to cool before adding eggs into it.
Next, mix in the dry ingredients: flour, custard powder and baking powder. Add them to the cooled butter mix and stir until combined. Pour in the vanilla and fold in the white chocolate, before pouring the mix into baking tin.
Add dollops of rhubarb compote and custard on top of the batter, and use a cocktail stick or a toothpick to create the marble pattern with it.
If you are using 8 x 8 inch baking tin, bake them for 45-50 minutes or until the edges are coming away from the tin and the mixture is set. For fudgy and gooey blondies, toothpick inserted in the middle should not be dry and should have some crumb attached to it. Just like with my homemade brownies ,these blondies will continue to cook and set as they cool.
If you prefer more cakey texture, bake them for 5-10 minutes longer.
I also baked these in rectangular, 20cm x 30cm (8' x 12') baking pan. As it is shallower and has larger surface, baking time will differ. For fudgy and gooey texture, you will bake them for about 35- 40 minutes. Add another 5-10 minutes for more cakey texture.
If your bake starts catching a bit of colour too quickly, cover it with some kitchen foil. Remove baked blondies from the oven, let them cool down in the tin, and drizzle with some melted white chocolate (optional). Transfer your baked blondies to the fridge for minimum of 2 hours, or overnight.
Just like good brownies need time to set properly, these blondies will also require some time to cool down, firm up and set. If you try slicing them while they are still hot, the bake will more likely fall apart. So it's important to allow them at least good couple of hours in the fridge.
You can store these in the airtight container for up to 3-4 days. The blondies will also freeze well. Make sure to wrap each slice well, then transfer to freezer-friendly container. freeze the individual Defrost them overnight in the fridge.
I don't like rhubarb, can I use anything else instead?
You can replace rhubarb with some other fruits like strawberries, cranberries, quinces, raspberries or sour cherries. You want to use something that is a bit tart and sharp in flavour, balanced with bitterness and sweetness. Favourite jam could also be used in place of rhubarb.
Alternatively, you may want to try some of my other blondie recipes, like these Chocolate Chip Walnut Blondies or readers favourite Biscoff White Chocolate Blondies.
Can I use different size baking tin?
Yes you can. Just remember that baking times will vary for different sizes. I tested this recipe in 8'x 8' square baking tin, 8' x 12' rectangular tin, and 9' round baking tin.
Why my blondies look under-baked?
Blondies, just like brownies should be taken out of the oven, when they are still slightly under-baked. This is because they will continue to cook and set after you take them out of the oven. That is what gives them fudgy and gooey texture. If you prefer yours to be more cake-like, then simply add few more minutes to the baking time.
Help, my blondies are not fudgy and really dry!
You have over-baked your blondies. Next time, simply reduce the baking time and perform the toothpick test to make sure it comes out with some crumb attached to it.
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Rhubarb and custard blondies
- 8' x 8' baking tin
- baking parchment
- rubber spatula
- 225 g butter plus some extra for the tin
- 200 g light brown soft sugar
- 100 g caster sugar
- 150 g plain, all- purpose flour
- 50 g custard powder
- ½ teaspoon baking powder
- 3 medium eggs
- 250 g white chocolate chips (or finely chopped white chocolate)
- 2 teaspoon vanilla extract
For the rhubarb and custard topping:
- 200 g rhubarb chopped into 3-4 cm pieces
- 75 g caster sugar
- 4 tablespoon ready- made custard or make it from custard powder
To make rhubarb and custard topping:
- Place the chopped rhubarb into a wide pan with caster sugar and 2 tablespoon of water. Cook on a medium heat, stirring frequently, for about 10 minutes, or until the rhubarb breaks down and turns jammy. Set aside to cool. If you are using powdered custard only, make the custard topping now and set it aside to cool.
- Heat the oven to 180 C (160 C fan). Place the butter and both sugars in a medium pan over a low heat. Melt them together until smooth and glossy, remove from the heat and cool for about 10 minutes.
- In a large bowl, sieve together the flour, custard powder and baking powder. Butter the baking tin and line it with baking parchment.
- Beat the eggs into the cooled sugar and butter mixture, then fold in the dry ingredients, until you have a smooth batter. Stir in 150g of white chocolate chips or chopped white chocolate and vanilla. Pour the batter into the baking tin then use a teaspoon to swirl the rhubarb on top of the batter.
- Add dollops of custard, then swirl a skewer or a toothpick through the rhubarb and custard to create the marbled pattern. Bake for 40-50 minutes until set and the edges are coming away from the sides of the tin. If the bake starts to catch the colour too much, cover it with kitchen foil. Leave in the tin to cool, then transfer to the fridge for minimum 2 hours or overnight.
- Melt the remaining 100g of white chocolate chips or white chocolate and drizzle it over the cooled blondies. Cut into equal squares and enjoy!
Please note that all my recipes are developed and tested in metric grams. I recommend that you use digital scales for a more accurate results. I have provided a conversion to US customary in the recipe but please note that I haven’t tested using this method.
- You can add few drops of pink food colouring to your rhubarb compote to intensify the colour
- Instead of using fresh rhubarb, you can also use frozen or canned rhubarb (if using canned rhubarb, make sure to drain it first)
- If you are not a fan of rhubarb, you can swap it for your favourite jam or fruit like strawberries, raspberries, quince, tart apples or cranberries.
- Store any leftovers in the airtight container in the fridge for up to 4 days. You can also freeze these blondies. Make sure to wrap each slice individually with clingfilm, transfer to the freezer-friendly container and place in the freezer for up to 3 months. Thaw in the fridge overnight.
This post was originally published in February 2020. It has been updated with new photos and tips in June 2021.
These were so good!
Glad you enjoyed them Audrey!
The white chocolate was such a nice touch
Thank you Audrey, glad you liked that!
You're right! Rhubarb and custard together are SO GOOD!
Thanks Amy, it's one of my favourite flavour pairings!
I think I might have to dig out the rhubarb from the freezer and make these, stat! Gosh, these look and sound incredible and really give me those spring feels!
Yaaas Nicole! Do it! 😉 Frozen rhubarb will work very well in this recipe! And yes, not long now until spring and all the fresh new produce that comes with it!
This is so so good. I love rhubarb based desserts and these look just perfect.
Thank you Sophie! I'm also a huge rhubarb fan, can't wait to bake some more with it this season!
Fabulous looking blondies that I can't wait to have in front of me - the looks, the anticipation of making them and the recipe itself (so easy to follow) - everything is perfect!
Hey Elaine! Thanks for stopping by! That's so sweet of you, I hope you will try this recipe soon and enjoy it as much as I do! Hugs!
Your pics are amazing!!!! I love the one of all the square flat and the one in the middle tuned so you can see the inside. I adore rhubarb and these sound so delish!
That is so lovely of you, thanks Daniela! So happy that you like the photos and the recipe! Have a great week ahead!
You photos are absolutely beautiful and the recipe looks delicious! Such a great flavor combination, will try to make it this weekend!
Thanks so much Veronika, let me know how you've enjoyed this recipe! Hugs!
I adore rhubarb and this might be one of the best ideas ever! Love how you used it! And the photos are fantastic. Thanks for sharing!
Hey Paula, thanks so much for your kind words! So happy that you like the recipe, rhubarb works so well in here, not overpowering, just enough to add a lovely taste and texture!
I've never seen blondies that look as perfect as these do! These look amazing!
Thanks Leslie, that's so sweet of you! I hope you will try this recipe and love it as much as I do!
These Blondies look fantastic. What a great dessert to try. Your pics are awesome.
Thank you so much! Hope you will try them some time soon!
These look so beautiful and delicious, my sweetheart! 😍 love your photos so much! ❤️
Lots of love,
Hi Bianca, thanks so much for stopping by and your lovely comment! I always drool over your food and photos! Big hug, have a great rest of the week!
These blondies have gotten a fresh fruit update! These would make a great dessert for the Spring holidays.
Hey Sharon, thanks for stopping by! They really do make great dessert, that jammy rhubarb and custard combo is a match made in heaven!