Preheat oven to 350°.
Combine first 3 ingredients in a bowl; stir well. Cut in 1/4 cup margarine with a pastry blender or 2 knives until mixture resembles coarse meal. Sprinkle ice water, 1 teaspoon at a time, over surface; toss with a fork until moist. Gently press dough into a ball. Divide dough into 20 equal portions, and press each portion into (1 3/4 inch) miniature muffin cups; set aside.
Place chocolate chips, peanut butter chips, and 1 tablespoon margarine in a small saucepan over low heat until mixture melts, stirring frequently. Remove from heat; add 1/3 cup sugar and milk, stirring with a whisk until well blended. Add egg substitute and vanilla; stir well.
Spoon about 2 teaspoons chocolate mixture into each prepared tart shell. Bake at 350° for 20 minutes. Let cool in pans 15 minutes on a wire rack. Loosen tarts from sides of pans, using a knife or narrow metal spatula. Remove from pans; let cool completely on wire racks.