Heat oven to 400°F. Line cookie sheet with parchment paper. Unfold pastry; roll to 12x11-inch rectangle. Cut 1-inch-wide strip from each side to make 4 strips. Cut 2-inch long piece from each strip; discard pieces.
Place pastry rectangle on paper-lined cookie sheet; prick with fork. Brush pastry with beaten egg white. To build up sides, place pastry strips on top of rectangle along edges, without overlapping; brush with egg white. Refrigerate while preparing filling.
In small bowl, combine flour, sugar, brown sugar, apple pie spice and lemon peel. With pastry blender or fork, cut in margarine until mixture resembles coarse crumbs. Sprinkle half of mixture over pastry. Arrange apple slices on top, overlapping slightly. Sprinkle with remaining crumb mixture.
Bake at 400°F. for 18 to 22 minutes or until pastry is golden brown and apples are tender. Cool 5 minutes. Drizzle warm galette with 2 tablespoons butterscotch ice cream topping. To serve, top with whipped cream and additional butterscotch topping.