Preheat the oven to gas 4, 180ºC, fan 160ºC. Tip all of the berries into a 1.5 litre baking dish and sprinkle with the sugar. Put in the oven while you make the topping.
Whizz the butter, flour and sugar with the vanilla and then add enough of the milk to make a soft, spoonable consistency (though make sure it isn't too runny).
Take the dish out of the oven and spoon scoops of clotted cream on top of the berries, then spoon scoops of the topping mixture right on top of the clotted cream. Sprinkle the demerara sugar over the top. Bake for 25 minutes or until the topping is golden brown and the berries are bubbling.