Preparation: 20 minutes + 1 hour chilling + cooling time
Cooking: 50 to 60 minutes
Total: 70 to 80 minutes + 1 hour chilling + cooling time
250g softened butter
125g caster sugar
125g light brown soft sugar
2 egg yolks
300g plain flour
3 tbsp cocoa powder
1 tsp baking powder
400g plums, halved and stoned
60g dark chocolate, coarsely grated
Cream to serve
Place the butter and sugars in a bowl and whisk with a handheld electric whisk for two to three minutes until creamy, then beat in the egg yolks, one at a time.
Add the flour, cocoa and baking powder and stir in until the mixture starts to form a dough. Tip onto a lightly floured surface and knead until smooth. Divide into two thirds for the bottom of the tarte and one third for the top. Wrap the dough in clingfilm, chill the larger piece for 30 minutes and place the other piece in the freezer.
Preheat the oven to 160C, gas mark 3. Grease a 25cm loose-bottomed tart tin then place on a baking tray Roll out the chilled pastry into a 30cm round on a lightly floured surface and use to line the prepared tin. Place the plums cut side up on the pastry and sprinkle over the grated chocolate.
Coarsely grate the frozen pastry over the plums. Bake for 50 to 60 minutes until the topping is crisp and the plums are tender. Cool for 30 minutes before removing from the tin. Slice and serve warm with cream.