Sift the flour into a bowl and rub in the butter to make 'breadcrumbs'. Stir in the sugar.
Beat the egg yolks and orange rind together then pour into the flour mixture. Mix gently with a round-bladed knife then mould by hand into a soft dough. If necessary, add a little cold water.
Wrap in clingfilm and place in the fridge for 20 minutes before rolling out. Preheat the oven to 190°C.
On a lightly floured surface, roll out the pastry to about 3mm thick and stamp out 24 circles using a fluted cutter. NB The circles must be slightly larger than the holes in your tin. Place the pastry circles in two shallow 12-hole bun/tart tins and press lightly into shape.
Prick the surface of the bases lightly and blind-bake for about 15 minutes. Remove from the oven and add small spoonfuls of jam to each tart, taking care not to overfill. Place two slices of apple on top of each tart, return to the oven and bake for a further 5 minutes.