Heat oven to 190C/170C fan/gas 5. Tip the flour and sugar into a large bowl. Add the butter, then rub into the flour using your fingertips to make a light breadcrumb texture. Do not overwork it or the crumble will become heavy. Sprinkle the mixture evenly over a baking sheet and bake for 15 mins or until lightly coloured.
Step 2 of 3
Meanwhile, for the compote, peel, core and cut the apples into 2cm dice. Put the butter and sugar in a medium saucepan and melt together over a medium heat. Cook for 3 mins until the mixture turns to a light caramel. Stir in the apples and cook for 3 mins. Add the blackberries and cinnamon, and cook for 3 mins more. Cover, remove from the heat, then leave for 2-3 mins to continue cooking in the warmth of the pan.
Step 3 of 3
To serve, spoon the warm fruit into an ovenproof gratin dish, top with the crumble mix, then reheat in the oven for 5-10 mins. Serve with vanilla ice cream.