To make a lemon pie using Shirriff pie filling, first rehydrate the powder by combining it with 2 beaten egg yolks and 1/3 cup cold water. Add an additional 2 cups of boiling water, and place over medium heat while continuously stirring. When the mixture bubbles, allow to boil for 30 seconds, and then remove it from heat, and add 1 tablespoon of butter. Cool for 5 minutes, and then fill the pie with the rehydrated Shirriff pie filling mix.
To make lemon meringue pie using Shirriff pie filling mix, substitute the 1 1/2 cups of lemon pie filling mix that the recipe requires for one reconstituted packet of Shirriff mix. Place the mix into a 9-inch pre-baked pie crust.
Take the two egg whites separated from the yolks during the pie mix reconstitution process. Separate another egg, and discard the yolk. Beat all three egg whites until they appear frothy, and then add 1/2 teaspoon of cream of tartar; beat again, this time until the mixture foams. Slowly add 6 tablespoons of powdered sugar, and continue beating until stiff peaks begin to form. Spoon the meringue mixture on top of the Shirriff pie filling mix, making sure to seal the edges against the crust and form swirls and peaks on the meringue.
Bake for 10 to 12 minutes at 375 degrees Fahrenheit. Allow to cool at room temperature for at least an hour, and then place in the refrigerator to chill. When serving, use a knife warmed with hot water to slice the meringue.