Wash and drain the blackberries. Preheat the oven to 220 °C (428 °F).
Beat the eggs with 2 tablespoons of powdered sugar. Add the flour and milk and stir well until an almost liquid batter forms.
Butter an ovenproof dish and add the blackberries. Pour the batter over them. Place the dish in the preheated oven. Bake for 20 minutes, then sprinkle with the remaining powdered sugar and bake for 15 minutes more.