Butter 4 mini casseroles and sprinkle with the sugar.
Set aside.
In a large bowl, beat the eggs for a few seconds with an electric mixer at medium speed. Continue beating at medium speed, adding in this order: the sugar, butter, flour, baking powder, milk and vanilla extract.
Set aside.
Place the blueberries and raspberries in the mini casseroles.
Top with the egg mixture.
Bake in the oven for 40 minutes.
Remove from the oven and let cool for 10 minutes.
Sprinkle the clafoutis with icing sugar sifted through a fine sieve.