Can be prepared in less than 45 minutes.
Roll out the pastry 1/8 inch thick on a lightly floured surface, cut out two 7-inch rounds, and transfer them to a baking sheet. Peel, halve lengthwise, and core the apple, slice it thin crosswise, and arrange the slices, overlapping them slightly, on the pastry rounds. In a small bowl stir together the sugar and the cinnamon, sprinkle the mixture evenly over the apples, and dot the tarts with the butter. Bake the tarts in the middle of a preheated 400°F. oven for 25 minutes, or until the pastry is golden brown. Transfer the tarts to a rack, brush them with the jam, and serve them warm with the ice cream.