Combine peaches, sugar, flour and nutmeg in a Dutch oven; set aside to allow syrup to form (approx. 15 minutes). Bring peach mixture to a boil: reduce heat to low, and simmer 10 minutes or until peaches are tender. Remove from heat and stir in vanilla and margarine. Roll half of pastry to 1/8-inch thickness: cut into a circle to fit a 2-quart baking dish. Spoon half of mixture into lightly buttered baking dish; top with pastry. Bake at 475° for 12 minutes or until lightly browned. Spoon remaining peach mixture over baked pastry. Roll remaining pastry to 1/8-inch thickness and cut into 1-inch strips; arrange in lattice design over peaches. Bake an additional 15-20 minutes until browned. Allow to cool slightly before serving. Serve with vanilla ice cream.