This crumble will make a great dessert for the whole family – the topping is generous so there will be plenty to go around. You can use either cooking or eating apples – cooking apples collapse when cooked, whereas eating apples will keep their shape and texture, so choose your favourite or simply use up what you’ve got.
To make the filling, put the apples in a large saucepan and drizzle over the lemon juice and 4 tablespoons of water. Stir in the caster sugar, using 75g/2¾oz for eating apples or 95g/3¼oz for cooking apples.
Cover with a lid and place the saucepan over a medium heat. Cook for 5 minutes, stirring occasionally, until syrupy and softening. Take off the heat, stir in the rhubarb and tip the mixture into a wide 2 litre/3½ pint baking dish.
Preheat the oven to 190C/170C Fan/Gas 5.
To make the topping, place the flour, cinnamon, butter and sugar in a large bowl. Rub together with your fingertips until it has a rough, crumbly mixture. Scatter the crumble over the top of the fruit, then sprinkle with 1 tablespoon of sugar.
Bake the crumble for 35–40 minutes until the top is golden and crisp and the fruit underneath is bubbling. Leave to cool for 10 minutes before serving with ice cream, cream or custard.