For the blueberry cupcake smileys, mix butter, sugar, vanilla sugar and add the eggs.
Stir in flour, baking powder and milk and fold in 2/3 of the blueberries.
Line a muffin tray with paper cups and spread the batter evenly. Bake at 175 degrees (convection oven 150 degrees) for about 25 minutes.
Prepare a thick glaze from lemon juice and powdered sugar and coat the cooled muffins with it.
Decorate smiley faces with blueberries and red rubber string – the blueberry cupcake smileys are ready.