For the yeast dough, melt 50 g butter at low heat. Add milk. Mix 500 g flour, 70 g sugar and 1 pinch of salt in a mixing bowl. Crumble the yeast into the milk and dissolve in it. Add lukewarm milk mix and egg to the flour.
Knead with the dough hooks of the mixer to a smooth dough. Cover and leave to rise in a warm place for about 45 minutes.
In the meantime, wash, clean and finely dice the strawberries for the filling. Roughly chop the chocolate. Knead the yeast dough again and roll out on the floured work surface (approx. 30 x 50 cm). Spread 50 g butter as evenly as possible on the dough.
Sprinkle with 5 tablespoons of sugar, strawberries and chocolate. Roll up the dough from the long side and cut into 3-4 cm wide snails.
Preheat oven (electric cooker: 225 °C/circulating air: 200 °C/gas: see manufacturer). Grease a flat casserole dish (approx. 28 cm long) and a springform pan (26 cm Ø). Place the snails in the moulds with the cut edges facing upwards and leave to rise in a warm place covered for another 30 minutes.
Bake in a hot oven for about 20 minutes. Remove from the oven. For the icing, mix sour cream and icing sugar with the whisks of the mixer until smooth. Spread the icing on the snails with a tablespoon and let it cool down.
Marinated strawberries taste good with it.