Preheat oven to 375F.
Butter 2 4 inch round baking dishes.
Start by making the sauce aka the juiciest filling by combining fruits, cornstarch, lemon juice, and brown sugar in a small saucepan. Cook on medium heat until the mixture thickens. This will happen fast, so make sure to stir the mixture regularly. Remove from the heat and divide evenly into 2 buttered baking dishes, dot with butter.
Place the flour, sugar, baking powder, and salt in a large bowl. Mix well with a spoon. Add butter (cut into cubes) into the flour mixture and gently stir (either with a spoon or your hands) until you have crumbs. Now, slowly stir in half of the cream, stir. Then add the other half. By adding the cream slowly and little by little helps to keep the crumbs in shape. Pour the mixture evenly over the raspberries and mango. Sprinkle a bit of brown sugar over the topping. (Optional)
Transfer to the oven and bake for 25-30 minutes at 375F until topping is golden brown and filling bubbly.
Take out from oven, let it cool a bit, then top with vanilla ice cream, more berries and enjoy!