Prepare the apples: Peel, core, and slice apples evenly. Place them in a bowl with lemon juice to prevent browning. Toss to coat well.
Blanch the apples: Boil a large pot of water. Add apple slices in batches, blanch for 1 minute, then remove and set aside.
Make the syrup: In a separate large pot, combine sugar, cornstarch (or Clear Jel), cinnamon, nutmeg (if using), and water. Whisk until smooth.
Cook the syrup: Bring the mixture to a boil over medium-high heat, stirring constantly until it thickens and begins to bubble.
Add apples: Gently fold the blanched apples into the thickened syrup. Simmer for 3–5 minutes to blend flavors.
Fill jars: Pack the hot apple pie filling into sterilized canning jars, leaving 1-inch headspace. Wipe rims clean and seal with lids and bands.
Process jars: Place jars in a boiling water canner. Process for 25 minutes (adjust for altitude if needed).
Cool and store: Remove jars, let cool for 12–24 hours. Check seals. Store sealed jars in a cool, dark place.