Prepare pastry for double-crust pie. On a lightly floured surface roll out half the pastry to a 12-inch circle. Line a 9-inch pie plate with the pastry. In a large bowl stir together sugar, cornstarch, almond filling, lemon juice, nutmeg, and salt. Stir in rhubarb and strawberries. (If using frozen fruit, let mixture stand for about 30 minutes or until fruit is partially thawed, but still icy.)
Transfer mixture to pastry-lined pie plate. Trim pastry to edge of pie plate. Dot filling with margarine or butter. Roll out remaining pastry to a 12-inch circle. Cut slits in remaining pastry; place on filling and seal. Crimp edge. To prevent overbrowning, cover edge of pie 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 for 20 minutes more. Quickly brush top with egg white and sprinkle with almonds; bake 5 to 10 minutes more or until top is golden and filling is bubbly. Cool on a wire rack. Makes 8 servings.
Pastry for Double-Crust Pie
In a medium mixing bowl stir together all-purpose flour and salt. Using a pastry blender, cut in shortening until pieces are pea-size. Sprinkle 1 tablespoon water over part of the mixture; gently toss with a fork. Push moistened dough to side of bowl. Repeat, using 1 tablespoon water at a time until all the dough is moistened. Divide in half. Form each half into a ball. Use as directed in pie recipe.