Dissolve the yeast and vanilla sugar in the lukewarm milk. Mix the flour, eggs and salt, then add the yeast milk while stirring constantly and mix into a dough. Then knead the very soft butter into the dough.
Let rise in a warm place for 45 minutes. Finally fold in the granulated sugar.
Bake each waffle at maximum temperature for 3 minutes in a waffle iron for Liège waffles.