CRUST Combine flour and 2 tablespoons sugar in a bowl; cut in margarine with a pastry blender until mixture resembles coarse meal. Sprinkle ice water, 1 tablespoon at a time, over surface; toss with a fork until dry ingredients are moistened and mixture is crumbly. (Do not form a ball) Press mixture into a 4 inch circle on heavy duty plastic wrap, and chill 15 minutes. Roll dough, still covered, to an 11 inch circle. Place in freezer 10 minutes or until plastic wrap can be easily removed. FILLING Combine apples, 1 tablespoon sugar, and lemon juice in a bowl; toss well. Let stand 15 minutes. Wrap handle of a 10 inch heavy skillet with aluminum foil. Sprinkle remaining 1/2 cup sugar in skillet, and place over medium heat. Caramelize by stirring often until sugar melts and is golden (about 6 minutes). Add apple mixture, and cook 5 minutes or just until apples are tender, stirring constantly. Remove from heat. Remove plastic wrap from dough. Place dough on top of apples in skillet, gently tucking dough around edge of skillet. Cut slits in dough for steam to escape. Bake at 425 degrees for 20 minutes or until browned. Invert onto a serving platter. SAUCE Combine brown sugar, yogurt, and sour cream; stir well. Drizzle over warm tart.