Mix the yeast, 1 tablespoon of the sugar and the lukewarm milk in a bowl. Leave to rise in a warm place for 5 minutes.
Melt the butter. Mix in a bowl with the flour, the yolk and 4 tablespoons of sugar. Add germ mixture, knead first with the dough hook of the mixer, then by hand for 5 minutes until smooth.
Chop chocolate.
Divide dough into 6-8 pieces and form balls. Form them into a flat oval shape. Spread some jam in the center and sprinkle chopped chocolate on top. Fold buns together and press ends down well.
Place in small loaf pans and cover with a kitchen towel. Let rise in a warm place for 1 hour.
Preheat oven to 160 degrees.
Mix yolks and whipped cream and brush the buns with it. Sprinkle with hail sugar and bake for about 15 minutes until golden brown. Serve lukewarm.