Mix flour, cocoa powder, sugar, yeast, and salt in a bowl.
Add milk and eggs, then knead the dough.
Add room-temperature butter and knead until the dough becomes smooth.
Shape the dough into a ball and let it rise for the first fermentation.
Divide the dough and shape into balls.
Place on a baking pan and let rise for the second fermentation.
Brush the surface with milk and bake in a preheated oven at 180°C for 20 minutes.