Prepare filling by mixing chocolate spread, cocoa powder, and yogurt to get a thick smooth consistency
Combine 350g bread flour, 150g cake flour, 70g granulated sugar, 6g salt, and 6g instant dry yeast
Mix 2 eggs with milk to make 285g total, add to dry ingredients and knead until smooth
Add 45g room temperature unsalted butter and knead until well incorporated
Shape into a ball, cover with plastic wrap, and let rise for 1 hour until doubled
Divide dough into 12 equal parts (74-75g each), shape lightly, and rest for 15-20 minutes
Shape dough into flat-topped rounds, cover, and let rise for 45-60 minutes
Remove plastic wrap and let surface dry for 10 minutes
Fry in 170°C oil for 2 minutes per side (4 minutes total)
While warm, make holes in donuts and coat with granulated sugar or sugar mixed with cocoa powder
Fill piping bag with custard cream and fill donuts generously
