Put the milk or half-and-half in an airtight container with the maple syrup, vanilla, and salt. Stir with a fork until the syrup dissolves.
Add the oats, stir a couple times, then smash the mixture into the bottom of the container in an even layer. Put the blueberries on top. Seal the container and refrigerate the oats for at least 8 and up to 16 hours.
If you want to turn overnight oats into hot oatmeal, transfer the soaked oat mixture to a microwave-safe bowl, cover, and cook on high until steaming, 1 to 2 minutes.
To eat hot or cold, stir the blueberries into the oats and decide if you want a little more milk. Serve, drizzled with more syrup.
—Recipe developed by The Bittman Project for Bob’s Red Mill