Mix the flour with the yeast and salt and quickly knead with the soft butter, egg yolks and milk to form a smooth dough. Let rest in the refrigerator for half an hour. Then roll out 4 equal parts into rectangles.
For the filling, beat the egg whites with powdered sugar to make snow. Spread on the rolled out pieces of dough, sprinkle a handful of nuts over each and roll them up thinly like sponge rolls. Use a knife to cut approx. 1-1.5 cm thick slices and place them on baking sheets lined with baking paper.
Bake the croissants in a preheated oven at 180 ° C for about 20 minutes, let them cool down and dust with powdered sugar.