Mix yeast and 15 g sugar. Melt 80 g fat in a saucepan, remove from heat and add the cold milk. Put 500 g flour, 60 g sugar, salt and egg into a mixing bowl. Add liquid yeast and lukewarm fat mixture and knead everything with the dough hooks of the hand mixer to a smooth yeast dough.
Cover and leave to rise in a warm place for 30-40 minutes. Meanwhile melt the remaining fat for the crumbles. Mix remaining flour and 100 g sugar and knead with the warm fat to a crumbly mass.
Knead the yeast dough again and form it into a roll on a lightly floured work surface. Cut into 12 pieces and form into oval, flat rolls. Place on two baking trays lined with baking paper and leave to rise for another 10-15 minutes.
Mix the egg yolk and 1 teaspoon of cream and spread on the rolls. Sprinkle with crumbles and bake in the preheated oven (electric: 200 °C/ gas: level 3) one after the other for 15-20 minutes.
Leave to cool on a cake rack and cut through horizontally once. Drain the peaches on a sieve and cut them into slices. Whip cream, remaining sugar and vanilla sugar until stiff.
Pour cream into a piping bag with a star-shaped spout and squirt cream onto each base. Cover with peach wedges and cover with the upper half. Arrange on a plate decorated with lemon balm.
Makes 12 buns.