1 For the cake: heat the oven to 180°C (160° fan) 350°F gas 4. Grease a 20cm|8" round cake tin and line the base with non-stick baking paper.
2 Beat the butter and xylitol in a mixing bowl until blended. Gradually beat in the eggs.
3 Sift in the flour and baking powder and stir in with the yoghurt until blended.
4 Spoon the mixture into the tin, spread level and place the apples and blackberries on top.
5 For the crumble: put the flour into a bowl and rub in the butter until the mixture resembles coarse breadcrumbs. Stir in the xylitol and a little water until the mixture sticks together in small crumbs. Sprinkle the crumble and almonds evenly over the fruit.
6 Bake for 30-40 minutes until the crumble is golden and the cake is cooked through. Cool in the tin for 10 minutes, then place on a wire rack to cool completely.