Blackberry Yoghurt Crumble Cake 

1. Heat your oven to 160°C fan. Line an 8 inch spring form cake tin with butter and parchment. 

2. Make the streusel topping by dicing your butter into small cubes, and getting them in a bowl with the flour. Rub together with your fingers until the mixture looks like breadcrumbs clumping together, then add the sugar and mix until just combined. 

3. Make the cake. Sift your flour and baking powder into a medium sized bowl. 

4. Add your caster sugar, vegetable oil, eggs, yoghurt, vanilla bean paste and the grated zest of your lemon to a large mixing bowl, and whisk until combined. Add your dry ingredients, and whisk in one direction until just combined. 

5. Toss 2/3rds of the blackberries with the remaining 1 tbsp flour, then add these to the mix and gently fold them in. 

6. Pour the mixture into the cake tin, then smooth out the surface with a rubber spatula. Sprinkle the remaining blackberries on top, as well as the streusel topping then bake for 1 hour. To check if it is cooked, insert a metal skewer through the middle. If there is any batter on the skewer, return to the oven for 10 minutes. 

7. Allow to cool in its tin before eating, with another dollop of yoghurt if you like.