In a large bowl stir together sugar, cornstarch, almond filling, lemon juice, nutmeg, and salt. Stir in the rhubarb and strawberries. (If using frozen fruit, let the mixture stand about 30 minutes or until fruit is partially thawed, but still icy.) Transfer mixture to the pastry-lined pie plate. Trim the pastry to the edge of pie plate. Dot filling with margarine or butter.
For top crust, roll out remaining pastry to a 12-inch circle. Cut slits in top crust; place on filling. Seal and flute the edge. To prevent overbrowning, cover edge with foil. Place pie plate on a baking sheet to catch any drips.
Bake in a 375 degree F oven for 25 minutes for fresh fruit (50 minutes for frozen fruit). Remove foil. Bake pie for 25 to 30 minutes more or until top is golden brown. Before last 10 minutes of baking, quickly brush top with egg white; sprinkle with almonds. Cool on a wire rack. Makes 8 servings.
Pastry for Double-Crust Pie
In a medium bowl stir together flour and salt. Using a pastry blender or two knives, cut in shortening until pieces are pea-size. Sprinkle 1 tablespoon cold water over part of the mixture; gently toss with a fork. Push moistened dough to sides of bowl. Repeat, using 1 tablespoon cold water at a time, until all of the dough is moistened (6 to 7 tablespoons water total). Divide in half. Form each half into a ball.