Put the flour and caster sugar in a bowl, add the butter and rub in with your fingertips until the mixture resembles coarse breadcrumbs. Gradually mix in enough of the eggs to bring the pastry together. Knead very lightly into a dough. Cover with clingfilm and chill for 30–45 minutes.
Roll two-thirds of the pastry out on a lightly floured work surface. Use to line a shallow, 23 cm (9 inch) fluted tart tin, then fill with the jam. Roll the remaining pastry out to a thickness of about 5 mm (¼ inch), then cut strips about 1 cm (½ inch) wide. Lightly brush the rim of the pastry case with water. Arrange the pastry strips in a lattice pattern over the tart. Chill for 20 minutes until firm.
Bake on a baking sheet in a preheated oven, 200°C (400°F), Gas Mark 6, for 20–25 minutes until the pastry is firm and golden. Leave to cool on a wire rack, then remove from the tin and serve with a generous dusting of icing sugar. The tart will keep in an airtight container for up to 2 days.