Preheat the oven to 150F or the lowest temperature your oven will go, and line a 11 x 17 rimmed baking tray with parchment paper.
Place the fruit, lemon juice and sweetener (if using) in a food processor or blender and puree until the mixture is smooth.
Pour the puree onto the lined baking tray, spreading out evenly using a spatula.
Place on a low rack in the oven and cook until the fruit feels dry to the touch and peels easily from the parchment paper, about 6-8 hours.
Remove from oven and allow the fruit leather to cool completely, at least one hour.
Use a pizza cutter, knife or scissors to cut into thin strips with the parchment paper still intact. The parchment paper will carefully peel off when you’re ready to enjoy them.
Notes
Storage: Fruit leather is best stored tightly wrapped in the refrigerator. Theoretically, homemade fruit leather is shelf-stable at room temperature but any slight moisture left can make it mold.