Preheat the oven to Gas 7, 220°C, fan 200°C.
Finely slice the apple halves into equal size pieces, put in a bowl and gently toss with lemon juice to stop them going brown.
On a floured surface, roll out the pastry, and cut 10cm rounds with a pastry cutter or round a saucer with a knife. Or do the same with the ready rolled pastry. Place on a buttered baking tray. Arrange the apple slices on top in a circle, slightly overlapping and almost to the edge of the pastry. Brush with a little melted butter, then sprinkle with the caster sugar and cinnamon. Bake for 15-18 minutes until golden. Cool slightly.
Dust each tart with icing sugar. Serve warm with custard or vanilla ice cream.
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Haven't got time to cook this from scratch?
Try our ready-made version - Tesco Bramley Apple and Fresh Cream Sponge.