For the filling
- butter, for greasing
- 12-15 large ripe plums, stones removed, chopped
- ½ lemon, juice only
- 160g/5½oz caster sugar
For the crumble
Preheat the oven to 180C/360F/Gas 4.
Grease a 30cm/12in square ovenproof dish.
Place the plums and lemon juice into the bottom of the dish and sprinkle with the sugar.
For the crumble, in a bowl, rub together the flour, caster sugar, muscovado sugar and cold butter cubes. (It is important that the butter is cold, or you will end up making more of a dough than a crumble.) When a crumble has been achieved, add in the oats and lemon zest. Mix well.
Sprinkle the crumble mixture over the plum mixture in the dish, then bake in the oven for 40-45 minutes, or until the topping is golden-brown.
To serve, spoon out generous portions into bowls and serve with lashings of custard.
To freeze: wrap well in cling film and freeze for up to one month. To cook: preheat the oven to 180C/360F/Gas 4 and bake for 50-55 minutes, or until the topping is golden-brown and the filling piping hot.