Select the blueberries, wash and drain well. Put them in a bowl and pour the cassis over them. Melt the butter in a small pot and let it cool down a little. Mix flour, 15 g sugar, baking powder and salt in a bowl. Whisk buttermilk and eggs.
Pour into the flour mixture while stirring and mix to a smooth, thin wafer dough. Finally stir in liquid fat. Preheat waffle iron, grease well. Bake 8 waffles one after the other. Beat the egg whites until stiff, adding 240 g sugar. Line a baking tray with baking paper and place the waffles on top. Spread marinated blueberries on top. Put a blob of meringue mixture on each wafer. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 10 minutes.
Beat the egg whites until stiff, adding 240 g sugar. Line a baking tray with baking paper and place the waffles on top. Spread marinated blueberries on top. Put a blob of meringue mixture on each wafer. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 10 minutes. Remove and sprinkle with red sugar