• Sift the flour into the mixer bowl, add milk powder, yeast, cardamom and salt. Mix.

  Pour in the milk, sour cream, add the eggs and start kneading the dough.
• After a few minutes, the dough will become more uniform. Still kneading, start adding the soft butter one spoon at a time. Wait with adding the next portion until the previous one is fully incorporated.
• Knead the dough until it is smooth and shiny, about 10 minutes. The dough is quite loose and slightly sticky. This is how it should be, do not add flour, because the rolls will be dense and dry (I speak from experience).
• Cover the bowl with the kneaded dough tightly with foil or a damp kitchen cloth and set aside in a warm place until it doubles in volume. This will take approximately 1-1½ hours.

  You can also leave the dough to rise overnight in the fridge and bake the whole thing in the morning.
• Gently remove the risen dough onto a lightly floured countertop. Divide it into 10 parts, shape each into a ball and place on a baking tray lined with baking paper. Cover them with a damp cloth to prevent from drying out and leave them to puff for about 30-40 minutes.
  

Crumble

• Meanwhile, prepare the crumble. Pour flour and sugar into a bowl, add the vanilla essence and cold butter cut into small pieces. Rub everything together with your fingers until it comes together without any traces of dry flour and resembles small peas. Until ready to use, you can gather the crumble into a ball, cover it and keep it in the fridge.

Assemble and bake

• Preheat the oven to 180℃
• With the bottom of a glass, make a well in each risen brioche, brush them with the egg wash and top with 4 plum halves in each .
  
• Sprinkle each bun with plenty of crumble, pressing very gently so it doesn't fall off.
  
• Bake for about 20-25 minutes until golden brown.