Melt butter in a pot. Add milk and sugar and warm up lukewarm. Pour into a bowl. Dissolve yeast in it. Stir in eggs and flour. Cover and leave to rise in a warm place for about 1 hour.
Knead in 40 g of sugar crystals. Divide the dough into about 12 portions and form into balls. Bake one after the other in a preheated greased waffle iron for Belgian waffles until crispy. Arrange on plates, sprinkle with remaining sugar crystals.