Preparation
First, you need to preheat the oven to 350° F. Then, you need to prepare the lemon filling. For this, mix sugar with flour and cornstarch. Sprinkle some salt over this mixture and place it in a medium-sized saucepan. Then, add some water, lemon juice, and lemon zest. Cook this mixture over medium high heat. Ensure you keep stirring the same, till the preparation comes to a boil. Now, stir in the butter.