Peel, core, and slice apples into THIN slices, about ¼ inch (about ½ cm) thick. You can do this with a apple peeler/slicer, or with a peeler and knife.
Add the sliced apples, butter, brown sugar, and all spices and vanilla to a large pot.
Over medium heat, cook apples for 20 minutes until soft with a little bite to them.
Combine lemon juice, water, and cornstarch in a small bowl and whisk together. If you want a sweeter filling, use water in place of the lemon juice to equal almost ⅔ cup.
Pour into apple pie filling and stir over medium heat for 1-2 minutes until the filling is thickened.
Cool completely to room temperature (or refrigerate) before using in a raw pie shell.
Notes
Slow Cooker Instructions: Combine all ingredients in crock pot and cook on high for 2-3 hours until apples are tender and mixture is thickened, stirring occasionally. To Store: Refrigerate for up to 4 days, freeze for up to 3 months.