Shell the hazelnuts.

Grease a baking dish with the small pat of butter. Sprinkle 3 tablespoons of brown sugar over the bottom of the dish.

Wash and cut the plums in half. Place the fruit in the dish, cut side down.

Make the dough by mixing the flour, remaining brown sugar, butter, egg, and ground hazelnuts. Form into a ball and chill in the refrigerator for 15 minutes.

Roll out the dough and cover the fruit with it.

Bake at 350°F (180°C) for 35 minutes.