Bread Dough

1. Combine the flour, sugar, salt, milk powder, and instant yeast in the bowl of a stand mixer fitted with a dough hook, or in a large mixing bowl
2. Add the lukewarm milk and stir until a rough dough ball forms
3. Add the unsalted butter and knead for 10-15 minutes with the stand mixer, or approx 20 minutes by hand until smooth and elastic
4. Roll into a ball, place in a large greased bowl, and cover with plastic wrap
5. Place the bowl in a warm spot to proof for 60-90 minutes, or until doubled in size
6. Once doubled in size remove the dough from the bowl and punch out any air
7. Divide the dough into 8 equal portions and roll them into balls
8. Place the dough balls on a large baking sheet lined with parchment paper and cover them with plastic wrap
9. Place the tray in a warm spot to proof for 30-60 minutes, or until almost doubled in size

Topping

1. Preheat the oven to 180C/355F
2. Combine the milk powder, flour, baking powder, baking soda, and sugar together in a bowl and whisk to combine
3. Add the butter, milk, egg yolk, and vanilla and mix everything together until it forms a dough, add more milk if it's too dry
4. Divide the topping dough into 8 equal pieces and roll them into balls
5. Roll each ball out into a flat circle with a rolling pin and place it on each proofed bun
6. Brush the tops with the beaten egg yolk and bake for 15 minutes
7. Transfer the baked buns to a cooling rack and cool for at least 10 minutes before consuming
8. To serve: Slice the baked bun horizontally with a serrated knife, but not all the way, then place a thick slice of chilled butter in between to serve