Preheat oven to 400 degrees.
Line a baking sheet with parchment paper. Unfold the pastry on parchment paper and cut pastry into 12 total rectangles or squares (depending on the shape of your pastry).
Pierce a ½-inch border around the edge of each pastry with the tines of a fork, then pierce all over inside this border.
Arrange the apples on top of the pastry in overlapping rows, inside the border.
Brush apples with the melted butter and sprinkle with the cinnamon sugar.
Bake for 30 minutes.
Brush the melted jam over apples and bake tarts until golden, about 8 minutes longer.
Serve warm or at room temperature.