Photograph: Martin Poole
Preheat the oven to 180°C, fan 160°C, gas 4. Peel and core the apples and cut them into chunks, then toss in a 20 x 30cm ovenproof dish with the blueberries, orange zest, brown sugar, butter and 2 tablespoons of water.
For the crumble, tip the flour, oats and demerara sugar into a mixing bowl with a pinch of salt. Add the butter and rub it into the dry mixture using your fingertips (or whiz in a food processor), then tip into a bowl. Stir in the nuts and orange juice. Bring the mixture together into small clumps.
Top the fruit with the crumble – you don't want it to completely cover the fruit, leave a few spaces. Bake for 40-45 minutes or until the apples are tender, the blueberries have slightly burst and the crumble is golden.
Kitchen secret: have a bowl of clotted cream on the side to spoon on to your pud as you eat.