Preheat the oven to 220°C fan-forced with bottom heat (use the bread-baking function if your oven has one).
Make the frangipane: beat the butter and caster sugar until pale and creamy. Add the eggs and mix until combined. Fold through the almond meal and plain flour until smooth.
Unroll the pastry, leaving it on the baking paper and transfer it to a large baking tray. Use the whole sheet — no cutting, no trimming.
Spread the frangipane evenly across the centre of the pastry, leaving a 3–4cm border.
Slice each apple half thinly (about 3mm), keeping the slices together so each half fans naturally. Lay six apple fans across the frangipane in a checkerboard pattern.
Toss the frozen blackberries with the caster sugar, cornflour and lemon juice. Scatter them into the gaps between the apple fans — rustic is the point.
Fold the pastry border up and over the edge of the fruit, gently pleating as you go.
Brush the pastry border with egg wash and sprinkle generously with caster sugar.
Bake at 220°C fan-forced for 20 minutes, then reduce the oven to 200°C and bake for a further 15–20 minutes, until the pastry is deeply golden, the apples are tender and the berries are bubbling.
Serve warm with vanilla ice cream or cream.
