Blackberry crumble slices

Line a 20cm-square deep brownie tin with a long piece of baking paper – the ends should overhang the edges of the tin on both sides.

For the biscuit base, blitz the digestives into fine crumbs in a food processor, or put in a strong freezer bag and crush with a rolling pin.

Melt 100g of the butter and 40g of the caster sugar in a pan over a low heat, then add the biscuit crumbs. Stir to combine.

Tip the mixture into the tin then spread over the base in an even layer, pressing down with the back of a large spoon. Chill in the fridge to firm.

Meanwhile, make the blackberry filling. Heat the blackberries, apple sauce and remaining caster sugar in a pan, until the berries begin to soften. Take off the heat, then remove from the pan with a slotted spoon, draining most of the juice – save the juice to use in another recipe.

Gently squash the berries with a potato masher or fork. Remove the biscuit base from the fridge and spread the berry mixture over it. Return to the fridge.

Preheat the oven to 180C/160C Fan/Gas 4.

In a large mixing bowl, rub the flour and the remaining butter together using your fingertips. When it begins to resemble breadcrumbs, add the demerara sugar and stir to combine.

Remove the tin from the fridge and sprinkle the crumble topping mixture evenly over the fruit filling.

Bake for 25-30 mins until the crumble is golden brown at the edges.

Allow to cool fully in the tin, then remove carefully, using