Place the milk in a small saucepan and heat it up until it is lukewarm. Add cubed butter to the lukewarm milk, swirling the saucepan every now and then to encourage the butter to melt. Remove from the heat and set aside.
In a bowl of a freestanding mixer fitted with a hook attachment, mix together the flour, sugar, salt and yeast. Add milk and butter mixture followed by the egg. Mix on low speed until dough comes together, about couple of minutes, then increase the speed to medium and and mix for 8-10 minutes until you have a smooth and elastic dough that no longer sticks to the sides of the bowl.
Transfer the dough to a lightly floured surface and using your hands, roll it into a ball. Place it in a clean, large bowl, lightly greased with some olive oil. Cover the bowl with clingfilm or reusable kitchen wrap (clean shower cup works great here!) and leave somewhere warm for an hour or until it doubled in size (depending on the temperature in your kitchen, this may take more, or less than 1 hour).
In a meantime, prepare the filling. Place softened butter and brown sugar in a bowl of a freestanding mixer and beat together on medium speed until pale, fluffy and well combined. Reduce speed to low and add ground cinnamon. Mix until combined and set aside.
Remove the dough from the bowl into a lightly floured surface. Gently knock out the air from it, then stretch it into rough rectangle shape. Using a rolling pin, roll the dough into larger rectangle, roughly about 40 x 50 cm, with the longer edge facing you.
Spread the filling over ⅔ of the top of the dough, leaving ⅓ of the dough clean. Fold the clean part of the rectangle towards the middle, then fold the other end of the dough on top of that (watch the video to see how easy it is!). Use a rolling pin, roll it over the rectangle to flatten it out and stretch a bit.
Using a sharp knife or a pizza cutter, trim off the edges of the rectangle. Divide the rectangle into 12 equal pieces, widthways, each strip roughly about 4 cm across. Next, use a knife or pizza cutter to cut twice down the length of each strip to make three strands. Plait the three strands together, then roll it up along its length to create a knot. Repeat with remaining strips.
Lightly grease 12-hole muffin tin, then transfer the knots into it. Cover and allow to prove for 45 minutes to 1 hour, or until they have doubled in size.
Preheat the oven to 170 C. Brush the knots with eggwash and bake in the middle shelf of the oven for 15- 18 minutes or until golden brown. Don't worry if some of the filling has leaked. Remove from the oven and allow them to cool only for a minute or so, then transfer the buns onto a cooling rack. Do not leave them to cool in the tin, as it will be hard to remove them later. Dust with some icing sugar (optional) and enjoy them while still a bit warm!
Do not go overboard with the filling! Thin, but even layer is what you are aiming for.
Don't worry if some of the filling comes out and spill from the sides while the buns bake. This is normal.
Once baked, allow the buns to cool in the tin for only a minute or so. Transfer them to cooling rack while they are still hot, before the leaked sugar and butter sets and becomes hard.
Make ahead instructions: Prepare the dough all the way up until step 5. Transfer to the fridge overnight. Next day, remove the dough from the fridge, let it sit at room temperature for 1-2 hours and proceed to step 5 in the recipe card. You can also place shaped buns in the fridge overnight. Cover the buns with plastic wrap or clean tea towel and place in the fridge. Next day, remove the buns from the fridge and allow them to sit at room temperature for at least an hour, then bake as per the instructions in the recipe card.