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

Method

1. 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.
2. In a medium bowl, thoroughly mix together the flour, polenta baking powder and salt.
3. 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.
4. 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.
5. 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.
6. Spread the cake batter evenly across the base of the prepared tin.
7. 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.
8. Then work the mixture with your fingertips until a coarse crumble is formed.
9. 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.
10. 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.