Roll out the puff pastry onto a large piece of parchment paper to 11 x 14 inches/28 x 35 cm. Brush the edge with water and fold over ½ inch/1.2 cm all around.
Poke the middle of the pastry with a fork all over. Use the parchment paper to lift and transfer the pastry to a baking sheet and bake for 10 minutes. This helps keep the pastry crisp under the fruit.
Arrange the apricot slices on the pastry. Brush pastry edges and apricots with melted butter and sprinkle evenly with the sugar. Bake for 10 minutes. You don’t want the pastry to brown. Remove from the oven and transfer to a cooling rack.
Heat the jam in a microwave-safe dish for 20 seconds until thinned out, stir, then brush all over the warm tart.
Slice and serve warm or room temperature with whipped cream and caramel sauce (both optional).