- 250g unsalted butter, softened
- 250g caster sugar
- Leaves from 5 sprigs fresh thyme
- 5 eggs
- 1 tsp vanilla bean paste or extract
- 300g plain flour
- 1.5 tsp baking powder
- 1/4 tsp salt
- 200g fresh rhubarb, cut into 5mm chunks
- 180g white chocolate chips
- 23cm/9-inch square baking tin, greased and lined with baking paper (or use a 23cm/9-inch square disposable foil container)
Preheat the oven to 170°C/150°C fan/Gas 4.
Place the butter, sugar and thyme in a mixing bowl and beat together until the sugar has dissolved into the butter, and the mixture is pale and fluffy. You can do this in a freestanding electric mixer fitted with a paddle attachment.
Add the eggs one at a time, and beat well after each addition, adding the vanilla with the last egg. Sift the flour, baking powder and salt over the top and fold in, then fold in the rhubarb and white chocolate chips.
Pour into the prepared tin and bake for 35–40 minutes, or until golden brown and a skewer inserted into the centre comes out clean – though don’t mistake a bit of soggy rhubarb or melted white chocolate for uncooked cake batter. Allow to cool in the tin.