Core the apple and peel if desired. Use a sharp knife to dice the apple or a box grater to grate it into small pieces.Optional: If you prefer softened apples, microwave the diced apples in a dish with 1 tablespoon water for 2 minutes, then allow them to cool and drain the water completely.
Divide the oats, diced apples, chia seeds, spices, almond milk, and maple syrup between two pint-sized mason jars or a large bowl or container. Mix the contents well with a spoon.
Cover and refrigerate the overnight oats for 6-8 hours. Stir the oats well before serving. You can eat them chilled directly from the fridge or warm them in the microwave.
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Notes
Makeit faster: To skip the overnight wait, microwave one serving of oats at a time, uncovered, for 2 minutes on High. Allow the oats to sit for another 2 minutes. Stir and eat right away!
Optionally, omit all the spices and substitute 1 teaspoon apple pie spice if you have it handy.
Storing leftovers: Overnight oats should be tightly covered or in an airtight container and stored in the refrigerator for up to 4 days.