To the bowl of your slow cooker, add the prepared apples, half of the water, sugar, lemon juice, spices, and butter.
10 apples, 1 cup water, packed 1/4 cup brown sugar, 2 tbsp lemon juice, 2 tsp cinnamon, 1/2 tsp nutmeg, 1/2 cup butter
Add the lid to the crockpot, and cook on high for 1 hour.
In a small bowl, whisk together the remaining half cup of water and the cornstarch until a uniform slurry's formed. Pour this into the apple mixture, stirring to combine.
2 tbsp cornstarch
Return the lid to the pot, and continue cooking for another 30-60 minutes- just until the apples are your desired level of tender and the sauce has thickened slightly.
Turn off the slow cooker, and allow the apple pie filling to cool completely. Stir it a couple times to prevent it from sticking as it cools.
Transfer the filling to glass jars and seal. Refrigerate for up to 2 weeks, and once opened use immediately.