Melt butter in a pot and stir in 230 g buttermilk. Mix flour, baking powder, vanillin sugar and sugar. Add milk butter and eggs and mix with the whisk of the hand mixer to a smooth dough.
Select fresh blueberries, wash and drain well. Place 1 tablespoon of dough on each baking surface of a preheated, greased Belgian waffle iron (approx. 12 x 21 cm) and sprinkle with some blueberries. Bake the waffles until golden brown. Let the finished waffles cool on a cake rack. Mix 1 tablespoon buttermilk with icing sugar to a glaze and drizzle over the waffles.