Method
Prep:15min  ›  Cook:20min  ›  Ready in:35min 

1. For the base: Preheat oven to 180 C / Gas 4. Grease or line a 23cm springform cake tin.
2. In a medium bowl, blend together the butter, dark brown soft sugar and flour with a fork until mixture resembles coarse crumbs. Press mixture into bottom of tin and bake for 20 minutes.
3. Cool completely before assembling.
4. To assemble the ice cream cake: Remove 1L of ice cream from the freezer and let it soften, but do not allow to melt. Spoon into a large bowl.
5. Add the frozen blueberries, using a large metal spoon, gently folding the mixture and crushing the berries a bit, until well combined. Spoon this ice cream mixture on top of the cooled base.
6. Cover and return to freezer for 30 minutes to firm up the first layer, then repeat for the remaining 1L of ice cream and raspberries. Cover and freeze for 4-6 hours before serving.
7. For the sauce: Combine all ingredients in a small saucepan. Stir over medium heat until cornflour dissolves. Cook until thickened, stirring occasionally, for 3-4 minutes. Let cool, then cover and refrigerate.