Preheat the oven to 180C/350F. Prepare a keto pie crust or use a store bought pie crust.
In a large mixing bowl, combine the chopped apples, butter, lemon juice, sweetener, flour, and cinnamon, and apple extract and mix well, until combined. In a separate bowl, mix your crumble topping together.
Transfer the apple pie filling into the pie crust. Bake the pie for 20 minutes, before removing it from the oven. Top with the crumb topping and bake for a further 15-20 minutes, or until golden brown.
Remove the pie from the oven and let sit for 5 minutes, before serving.
Notes
TO STORE: Apple pie must always be stored in the refrigerator, covered. It will keep well for up to 2 weeks.TO FREEZE: Place leftovers in a sealable container and store them in the freezer for up to 6 months.REHEATING: Either microwave the pie for 30 seconds or heat in the oven at 180C/350F for 5-6 minutes, until warm.