Preheat the oven to 200C/400F/Gas 6. Put the hulled raspberries into your pie dish and sprinkle over the sugar, almonds and vanilla extract. Give the dish a good shake or two to mix the ingredients.
Now for the crumble topping: put the gluten free flour and baking powder in a mixing bowl and rub in the cold, diced lactose free butter between thumb and fingers (or in a freestanding mixer or food processor).
When you’ve finished, it should resemble rough, pale oatmeal. Stir in the oats and demerara sugar with a fork.
Tip the topping over the raspberry filling, covering the raspberries in an even layer and pressing the topping in a little at the edges of the dish.
Set the dish on a baking sheet and bake in the oven for 30 minutes, by which time the crumble topping will have darkened to a pale gold and some pink-red juices will be seeping and bubbling out at the edges.
Leave to stand for 10 minutes before serving, and be sure to put a jug of chilled lactose free double cream on the table alongside.