Preheat the oven to Gas Mark 7, 220°C, fan 200°C. Line two baking sheets with nonstick baking paper.
Unroll the puff pastry sheet, lay it on a work surface, then cut into 8 rectangles. Lightly score about 5mm (¼in) from the edges of each rectangle with a sharp knife, to give a narrow border. Lay them on the baking sheets. Spread ½ tablespoon of the lemon curd over the centre of each piece of pastry, just up to the border.
Lay the apple slices onto each piece of pastry so they overlap, standing up slightly, and cover the centre of the pastry, but leave most of the border uncovered. Bake for 15-18 minutes, or until the apples are just tender and the pastry edges are golden.
Meanwhile, for the glaze, warm the remaining 3 tablespoons of lemon curd in a small pan with 2 teaspoons of water, until it is just runny. Remove the tarts from the oven, and brush the apples and pastry edges with the glaze. Leave them to cool slightly, then serve warm with double cream or vanilla ice cream.