For the base: The biscuits are crushed in a bowl. They add powdered sugar and cocoa. Mix, then add the melted butter and milk and stir until a homogeneous mixture results. The resulting mixture is poured into a pan cake and put in refrigerator to set while doing banana mousse. For the mousse: blend bananas with sugar. Then put the egg whites and beat with a mixer for about 10 minutes, until a thick cream. Then pour the cream over the biscuit base and put back in the refrigerator until firm.