Preheat the oven to 170 C (160 C fan). Line 12- hole muffin tray with paper cases and set aside.
Sieve the flour, cinnamon, cardamom, baking powder and salt into a large bowl. Add both sugars and stir to combine. Add butter, apple sauce, yogurt, eggs and vanilla and mix until just combined, using an electric mixer.
Divide the batter between the cupcake cases, filling ¾ of each case with batter. (I use my ice-cream scoop for this step, to ensure the equal amount of batter in each case). Bake for 20-25 minutes until risen and golden brown, or until toothpick inserted in the middle comes out clean. Remove from the oven and cool the cupcakes completely.
To make blackberry buttercream:
Place blackberries into a blender and blend for 20 seconds. Push the puree through a sieve, discarding the seeds. Set the juice aside.
In a bowl of an electric mixer, mix together butter and icing sugar until smooth. Add 2- 3 tbsp of blackberry juice and mix until combined. Transfer the buttercream into a piping bag fitted with your favourite piping nozzle and pipe on top of cooled cupcakes. If buttercream becomes too soft, place it in the fridge for 10-15 minutes. Top each cupcake with fresh blackberry. Enjoy!
To make apple sauce, simply peel, core and chop 2 medium apples and place them in a small saucepan with 100 ml of water and 2 tbsp of caster sugar. Cover with lid and cook on a medium heat for 8-10 minutes, or until apples are completely tender and cook through.
Make sure butter is at room temperature. Not too cold, but not too soft either. I recommend taking it out of the fridge about 1 hour before baking. To test your butter, poke it with your finger. It should make an indent without sinking into the butter. Your butter should not be shiny or greasy, and it should be cool to touch.