Mix the milk with sugar, salt and butter and heat gently. Dissolve the yeast in it. Put the flour in a bowl and make a well in the middle. Pour the lukewarm liquid into the well and knead a yeast dough, if necessary add a little more flour until the dough is no longer sticky.
Shape a ball and let the dough rise in a warm place for about 1 hour until the volume has approximately doubled.
Chop the chocolate for the filling. Mix the hazelnuts, cinnamon, cocoa powder, sugar, vanilla sugar and chocolate. Mix in a little milk (approx. 3-5 tablespoons) so that a homogeneous, spreadable paste is created. A little less or a little more milk may be required for this. In no case should the paste become too runny.
Roll out the yeast dough into a rectangle (approx. 30cm x 40cm) and distribute the filling evenly on top. Roll up tightly from the long side. Halve the strand lengthways with a sharp knife so that 2 open strands are created. wrap the strands around each other so that the side with the filling is always on top.
Place on a baking tray lined with baking paper and cover with a damp cloth and let rise for another 30 minutes.
Bake at 190-200 ° C for about 30-40 minutes. If necessary, cover with some aluminum foil halfway through, if the braid gets too dark. The baking time can vary a little depending on the oven.