Preheat oven to 190°C (375°F) or 170°C (340°F) for fan ovens. Line the base of a 20 cm (8-inch) deep springform tin with baking paper and grease the sides.

Put the flour, ground almonds, lemon zest, and 125 grams of the caster sugar in a food processor. Pulse briefly to combine. Add the cold diced butter and pulse until the mixture resembles fine breadcrumbs. Don't overwork it or it will become dough.

Using a spoon, press half the crumble mixture firmly into the bottom of the prepared tin, packing it down like shortbread.

Mix the sliced apples with the remaining 75 grams of caster sugar and the blueberries. Spoon this fruit mixture evenly over the crumble base.

Scatter the remaining crumble mixture over the top, covering the fruit completely. It should come right to the top of the tin. The mixture will sink slightly as it bakes.

Bake for 60 minutes until the streusel topping is deep golden brown. If it's browning too quickly, loosely cover with foil for the final 15-20 minutes.

Let cool in the tin for at least 20 minutes before removing. The cake is delicious served warm or at room temperature.

Dust with icing sugar and serve with whipped cream or vanilla ice cream.