Mix both milks together in a bowl. Soak the gelatine in 4 tablespoons of water, and then dissolve in a bain-marie. Add to the milk, giving a good stir to make a creamy texture. Whisk the egg whites to firm peaks, and gently fold into the milk. Place a greased flan ring on a baking sheet lined with greased silicone paper. Sprinkle the crushed biscuits to form an even base inside the flan ring, and then pour the mixture over it, filling the circle to the top, and leave in the refrigerator until set. When ready to serve, invert a flat plate over the flan ring and turn the pudding over. Remove the silicone paper and the flan ring. The biscuit crumbs will now be on top.