Custard blueberry skillet buns

The base recipe for the dough used in this recipe is a standard wheat flour dough used for all manner of Swedish baked goods. However, I've noticed that Sweden doesn't seem to have the same 'custard culture' as Britain and recipes often tell you to simply use a store bought thick custard (marsankräm) for baking. So, I decided to improve a typical filled custard bun by using homemade crème patisserie here, making them vastly tastier. The blueberries are of course optional, but is there a better combination than blueberry custard?

Notes
Makes 20-30 buns | Prep: 1h 30min | Cooking: 15-20min

Dough
2 sachets fast action dried yeast (14g)
125g butter
250ml milk
1tsp cardamom, ground
2 eggs
50g sugar
500g flour (more can be added if needed)

Crème Patissiere
4 egg yolks
60g sugar
25g flour
2tsp cornflour
280ml milk
1tsp vanilla extract

Buttercream filling
100g butter
120g sugar

50g blueberries (frozen or fresh)
1tbsp demerara sugar
1 egg yolk
1tbsp milk

Instructions
Melt the butter and stir into the milk in a saucepan. Gently heat the mixture until it’s room temperature. Stir in the yeast and leave for a minute. Meanwhile, combine sugar, salt, flour, and cardamom and whisk the egg lightly. Mix everything into the yeast mixture and knead it until a dough is formed. Cover the dough with a kitchen towel and leave to rise for 45 minutes.

Continue to knead the dough until it is smooth and elastic. Divide it into two parts. Roll out one half to form the bottom and place in an oven proof skillet or dish lined with baking parchment (you can use either a round or rectangular one). Spread the crème patissiere over the dough.

Roll out the other half of the dough to a rectangle and spread the buttercream filling over it. Fold the dough over itself in half so that you have a double rectangle of dough. Cut the dough into 2cm strips.

Twist each strip into a knot to form a bun. I’ll admit that it’s quite difficult to clearly describe this part in writing, but there are plenty of Youtube videos that show various ways of doing it (here’s a good one that does it in a slightly more fancy way than mine).

Place the buns evenly over the bottom layer, making sure that there’s some room for them to rise. Beat together an egg yolk with a tablespoon of milk and brush the buns with the mixture. Scatter blueberries and demerara sugar over them.

Bake in the oven at 225c for 15-20 minutes. Allow to cool slightly before serving.