Warm the whole milk until lukewarm, then stir in the active dry yeast, 1 tablespoon of powdered sugar, and 1 tablespoon of all-purpose flour.

Leave the yeast mixture in a warm place for 10 minutes until foamy and expanded.

Combine the remaining all-purpose flour, powdered sugar, salt, egg white, vegetable oil, and activated yeast mixture in the large mixing bowl.

Knead the mixture until it forms a smooth, sticky dough.

Oil your hands and lift the dough from the bowl onto a lightly oiled work surface.

Cover the dough with plastic wrap and let it rise in a warm place for about 60 minutes.

Finely chop the dark chocolate if using a chocolate bar.

Knead the dark chocolate pieces into the risen dough until evenly distributed.

Divide the dough into 14 equal pieces and shape each piece into a small ball.

Roll each dough ball into a small round and place about 18 g of Nutella hazelnut cocoa spread in its center.

Seal the dough around the filling and reshape each portion into a smooth ball or roll.

Place the buns seam-side down on the baking tray lined with baking paper, then cover them with a clean kitchen towel.

Let the shaped buns proof for 20 minutes while the oven heats to 200°C.

Whisk the egg yolk with the milk for egg wash until smooth.

Brush the risen buns with the egg wash.

Bake at 200°C until deep golden brown, about 20 minutes.

Cool the buns briefly before serving warm, when the chocolate filling is soft.