Ingredients to make a 23cm round cake:
For the cake batter:
- 115g softened butter
- 115g plain flour
- 70g polenta
- 2 tsp baking powder
- a pinch of salt
- 90g golden caster sugar
- 90g sugar
- 2 large eggs
- 100g sour cream
- ½ teaspoon vanilla extract
- ½ teaspoon grated lemon zest
- 300g rhubarb, cut into 3-4cm chunks
For the crumble topping:
- 90g sugar
- 6 tablespoons plain flour
- 2 tablespoons polenta
- ½ tablespoon ground cinnamon
- 30g butter, cold, cut into small cubes
- Heat your oven to 180 degC and line the bottom of a 23cm springform baking tin with greaseproof paper. Grease the paper and tin sides with butter or oil.
- In a medium bowl, thoroughly mix together the flour, polenta baking powder and salt.
- In a large bowl cream together the sugars and the butter until they become a little fluffy. It takes a few minutes. Then beat in the eggs, one at a time: the mixture may curdle slightly but don’t worry.
- Then add a third of the flour mixture and blend together. Add the sour cream, lemon zest, vanilla extract and a further third of the flour mix, again thoroughly blending.
- Roll the chopped rhubarb in the remaining flour mix, tumbling the chunks around until coated. Then fold the rhubarb/flour mix gently into the batter until the flour is all wetted.
- Spread the cake batter evenly across the base of the prepared tin.
- In the (now empty) medium bowl, stir together the crumble dry ingredients – sugar, flour, polenta, cinnamon – and then drop in the butter cubes and roll around to coat them.
- Then work the mixture with your fingertips until a coarse crumble is formed.
- Sprinkle the topping evenly over the batter and bake the cake in the oven until the top is golden brown and a knife inserted near the centre comes out pretty clean. This will take at least 35 minutes and possibly as much as 50, depending on the moisture in the rhubarb.
- Remove from the oven and cool the cake in the tin on a rack for 10 minutes before running a spatula around the edge and releasing the spring. Lift the cake onto the rack and allow to cool.
Serve just as it is as a cake or with vanilla ice-cream or cream as a pudding.Dust the top with icing sugar before serving if you want to gild the lily.