Put flour into a bowl, create a well in the center and crumble the yeast, add sugar and pour in milk. Gently mix yeast and milk and let rest in a warm place for about 20 minutes.
Melt butter and combine with egg yolks. Add to flour mixture and knead, let rise about 20 minutes. Divide dough into 8 equal portions. Knead each portion, shape into a ball and let rise another 30 minutes. Boil water in a steamer and grease the steam tray with butter.
Put 3-4 pieces of dough in steamer. Cook for 15-20 minutes. Repeat with remaining dough. Melt butter in a frying pan, mix in breadcrumbs and vanilla sugar. Pour butter mixture on dumplings and serve.