Mix together the flour, baking powder and caster sugar in a bowl. Stir in the blueberries. Beat together the eggs, melted butter, milk and vanilla in a jug. Add to the dry ingredients and stir together using a large metal spoon until just combined.
Divide the mixture evenly between paper muffin cases arranged in a 12-hole muffin tray. Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for about 20 minutes until well risen and just firm to the touch. Transfer to a wire rack and sprinkle with vanilla sugar. Serve warm or cold.