Preheat the oven to 450°. On a lightly floured surface, roll out the pastry to a 16-by-10-inch rectangle. Transfer to a 15-by-10 1/2-inch baking sheet, trimming the excess dough. Arrange the apple slices in crosswise rows on the pastry. Spread the butter over the apples and sprinkle with the sugar. Refrigerate until the pastry is firm, at least 15 minutes.
Bake the apple pizza for about 15 minutes, or until the pastry is puffed and golden and the apples are glazed. Serve the apple pizza warm with vanilla ice cream.