Step 1: In a clean glass jar or container, combine the rolled oats, chia seeds, and a pinch of salt, stirring to distribute the seeds evenly.
Step 2: Add the milk, vanilla extract, and your choice of sweetener (maple syrup or honey) to the jar.
Step 3: If using Greek yogurt, add it now and stir well until all the oats are thoroughly moistened and no dry clumps remain.
Step 4: Gently fold in the blueberries. If using frozen berries, there is no need to thaw them first.
Step 5: Secure the lid on your container and place the blueberry overnight oats in the refrigerator for at least 4 hours, or ideally overnight.
Step 6: In the morning, remove the lid and give the oats a good stir. If the mixture is too thick, add a splash of extra milk.
Step 7: Top with extra blueberries, nuts, or a drizzle of nut butter if desired, and enjoy your blueberry overnight oats cold!