Place the peeled and sliced apples into a 4-quart or larger slow cooker.
Sprinkle the cornstarch over the apples and toss gently until the slices are evenly coated.
In a small bowl, mix together the brown sugar, cinnamon, and nutmeg.
Pour the sugar and spice mixture over the apples, followed by the lemon juice and vanilla extract. Toss again to combine.
Scatter the cubed butter over the top of the apple mixture.
Cover and cook on High for 2 hours, or until the apples are tender but still hold their shape. Stir halfway through cooking to redistribute the sauce.
Stir well before serving to coat the apples in the thickened syrup. Serve warm.