Preheat oven to 350. Mix 2 cups flour and 1/2 cup powdered sugar together. cut in margarine until mixture forms pieces the size of peas. Grease 11x14 inch pan. Press crust into pan. Bake at 350 for 20 minutes.
Beat eggs slightly. Add sugar and lemon juice. Fold in 4 tablespoons flour and baking powder. Pour into baked crust. Bake for 25 minutes. Sprinkle top with powdered sugar while still hot.