Apple Filling
In a medium saucepan over medium heat, melt butter and stir in the chopped apples, brown sugar, cinnamon, lemon juice, and a pinch of salt. Stir frequently until the apples are tender. In a small bowl, mix the cornstarch with a tablespoon of water to make a slurry. Pour the cornstarch slurry into the apple mixture and cook until thickened, then let cool to room temperature.