Butter (lactose free) and line a traybake or small roasting tin, about 20 x 30cm. Heat oven to 180C/160C fan/gas 4.
Gently melt the lactose free butter in a large saucepan, cool for 5 mins, add the sugar, vanilla and eggs, then beat until smooth with a wooden spoon. Stir in the gluten free flour, almonds and ¼ tsp salt.
Tip the mix into the tin. Scatter the raspberries and almonds over, then bake for 1 hr-1 hr 10 mins, covering with foil after 40 mins.
Test with a skewer: the middle should have just a tiny hint of squidginess, which will firm up once the cake cools.
Cool in the tin for 20 mins, then lift out onto a cooling rack. Once cold, dredge with icing sugar, then cut into squares