Fill a large canning pot or stock pot halfway with water and bring it to a simmer. Sterilize your jars, lids, and bands for canning.

Pack each jar tightly with apple slices, using a wooden spoon to press them in firmly.

In a separate pot, combine the cornstarch, sugar, nutmeg, cinnamon, and salt. Add water and cook on high, stirring frequently, until the mixture becomes bubbly and thickened.

Remove from heat, stir in the lemon juice, and pour the hot syrup into each jar, leaving about 1 inch of space at the top.

Wipe the rims of the jars clean, then place the sterilized lids and bands on securely.

Place the jars in the simmering water, ensuring they are covered by at least 1 inch of water. Bring the water to a rolling boil, cover, and process for 20 minutes.

Carefully remove the jars and place them on a towel to cool for 24 hours. Check the seals by pressing the center of each lid. Store the sealed jars in a cool, dark place for up to 18 months.