For this easy and cheap recipe, place a shortbread crust into your pie pan and bake for 20 minutes at 350 °F with a heavy pan on top to prevent it from puffing up. For the filling: In a saucepan, heat the juice and zest of 4 lemons, adding 3/4 cup sugar and 2 1/2 tablespoons cornstarch. Beat 3 eggs in a mixing bowl and add to the saucepan, stirring constantly. Pour the preparation onto the pre-baked pie crust. Beat 3 egg whites into soft peaks, then mix in 1 cup powdered sugar. Distribute evenly onto the pie, and bake for 10 minutes at 350 °F.