The day before, crumble the yeast into a small bowl and stir with 3 tablespoons of sugar until liquid. Melt 40 g butter in a small pot. Add milk and remove from the heat. Put 350 g flour, 1 pinch of salt, egg and yeast into a mixing bowl. Add the milk mixture and knead to a smooth dough with the dough hooks of the mixer. Cover and leave to rise in a warm place for about 45 minutes until the dough volume has doubled.
Cut 200 g butter into thin slices. Knead yeast dough briefly and roll out to a rectangle (approx. 35 x 38 cm) on a floured work surface. Cover half of the dough surface (approx. 17 x 38 cm) with slices of butter, leaving one edge free. Place the other half on top. Press the edges well together. Roll out the dough again to a large rectangle (approx. 35 x 38 cm) and fold it lengthwise in the middle. Wrap in cling film and chill for about 30 minutes. After the cooling time, repeat the last 2 steps (roll out and fold up) 4 times in total. Then put the dough in a cool place overnight.
The next day grease the twelve troughs of a muffin tray. Preheat the oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Cut dough sheet into 12 squares. Roll out each piece on a floured work surface to a long, slightly wider strip (approx. 9 x 33 cm). Spread 125-150 g soft butter on all dough strips. Roll up each strip from the short side. Cut each roll of dough in half lengthwise. Roll up each half and place on top of each other in the muffin tray. Bake in a hot oven for about 25 minutes. (If necessary, line the bottom of the oven with aluminium foil, as fat can leak out).
Remove the muffin tray from the oven and let the cruffins rest in it for about 10 minutes. Then lift them out of the trays and let them cool on a cake rack. Dust the cruffins thickly with icing sugar.