Position knife blade in food processor bowl; add first 3 ingredients, and pulse 2 or 3 times. Add margarine pieces, and pulse 10 times or until mixture resembles coarse meal. With processor running, slowly add ice water through food chute, processing just until combined (do not form a ball).
Gently press flour mixture into a 4-inch circle on heavy-duty plastic wrap; cover with additional plastic wrap. Roll dough, still covered, into a 15- x 13-inch rectangle. Place dough in freezer 5 minutes or until plastic wrap can easily be removed. Remove top sheet of plastic wrap. Invert and fit dough into a 2-quart baking dish coated with cooking spray, allowing dough to extend over edges of dish; remove top sheet of plastic wrap.
Combine peaches, 1/2 cup brown sugar, 2 1/2 tablespoons flour, vanilla, and cinnamon in a large bowl; toss gently. Spoon peach mixture into prepared dish; fold edges of dough over peach mixture (it will only partially cover peaches). Sprinkle remaining 1/4 cup brown sugar over peach mixture; sprinkle with almonds.
Combine egg and 1 teaspoon water in a small bowl; stir well. Brush egg mixture over dough, and sprinkle with 1 tablespoon sugar. Bake at 375° for 45 minutes or until filling is bubbly and crust is lightly browned. Let cobbler stand 30 minutes before serving.