You could use hazelnuts instead of cobnuts, but it's worth making the effort to find the real thing. They're plentiful at this time of year; if you find them hard to come by, you can get them by mail order from Jill Allen, 01732 812215 (cobnuts.co.uk). You'll have to shell the nuts before toasting them for 10-15 minutes at 180C/360F/gas mark 5½. Recipe serves six.

For the crumble:

175g plain flour
100g soft unsalted butter
3 tbsp cobnuts (or hazelnuts), toasted and finely chopped
1 tbsp custard powder
4 tbsp caster sugar
2 tbsp milk
½ tsp baking powder

For the filling:

300g ripe soft red plums, pitted and cut into small pieces
1 tbsp cornflour

3 tbsp caster sugar

Zest of ½ orange

Preheat the oven to 180C/360F/gas mark 5½. In the bowl of a food processor (or by rubbing quickly with nimble fingers), combine the ingredients for the crumble. Divide the mixture in half and place one portion, covered, in the fridge. Press the remaining portion into the base and sides of a lightly greased 20cm tart tin (with a removable base). In a bowl, stir together all the filling ingredients, then spread over the pastry. Finally, crumble the remaining pastry over the fruit and bake for 35-40 minutes, or until the fruit is bubbling and the top lightly browned. Remove from the oven and leave to cool before slicing.

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