Put the quartered apples in a bowl and shuffle them around to mix them up a bit. Mix the cinnamon with the sugar in a separate bowl. Put half the apples in an oven dish and sprinkle with a third of the sugar mixture. Add the blackberries and sprinkle with the second third of sugar mixture. Cover with the remaining apples and add the remaining sugar and cinnamon mixture.
To make the crumble topping: Put the flour and cinnamon in a bowl and mix well, then stir in the sugar and the oats. Cut the butter into small cubes, add to the mixture and rub it in with your fingertips until the mixture is the texture of breadcrumbs. Lay the crumble mixture on top of the fruit.
Preheat the oven to 170°C, gas 3 and bake the crumble for about 40 mins. Keep an eye on the top. The sugar should go golden, not black. Serve with homemade custard.
This recipe is taken from Mums Know Best: The Hairy Bikers' Family Cookbook, £20 from Weidenfeld & Nicolson. The book is also available from Amazon.co.uk. The Hairy Bikers: Mums Know Best is on BBC2 at 8pm everyday Tuesday, from 5th January 2010 for six weeks.