In a tall mixing vessel, beat the egg white until stiff, gradually stirring in the sugar until the egg whites are nice and shiny.
Mix the berry mixture with the vanilla sugar. Put in a large baking pan. Crumble the biscuits into small pieces with your fingers and place them on the berries. Finally, distribute the egg white with a tablespoon. Then bake on the middle rack in the oven for about 10 minutes until the egg white is golden brown. Finally dust with icing sugar and serve.