Mix the Ingredients: In a mixing bowl, combine the all-purpose flour, sugar, yeast, and sugar. In a separate bowl, mix warm milk, egg, vinegar, oil, melted butter, and vanilla sugar. Combine the wet and dry ingredients together and mix until a dough forms.

Knead the Dough: Transfer the dough to a floured surface and knead until it's smooth and elastic, about 10 minutes.

Rest the Dough: Place the dough in a lightly greased bowl, cover it with a cloth, and let it rest in a warm place for about one hour or until doubled in size.

Prepare Chocolate Filling: While the dough is resting, prepare your chocolate filling by mixing the chocolate with 50ml of warm milk.

Shape the Brioche: After resting, divide the dough into 9 equal parts. Take one part, flatten it, and place a spoonful of the chocolate filling in the center. Seal and form a ball. Repeat until all dough parts are filled.

Decorate and Proof: Take the reserved 50g of dough, mix with cocoa, and create strips to place on top of the chocolate balls. Place them in a greased mold, cover, and let rest for another hour.

Bake the Brioche: Preheat your oven to 180°C (350°F). Brush the brioche balls with the egg wash and bake for about 30 minutes or until golden brown.