Combine milk and oats. Set aside for 20 minutes so the oats puff up and soak up some moisture.

Preheat oven to 425°F (218°C). Spray a 12-count muffin pan with nonstick spray or use cupcake liners.

Whisk the flour, baking powder, baking soda, cinnamon, and salt together in a large bowl until combined. In another bowl, whisk the melted butter, honey, egg, and vanilla extract together until combined. Pour the wet ingredients into the dry ingredients, stir a few times, then add the soaked oats (milk included) and blueberries. Fold gently until combined.

Spoon the batter into liners, filling them all the way to the top. Bake for 5 minutes at 425°F, then reduce the oven temperature to 350°F (177°C) without removing the muffins. Bake for an additional 16-17 minutes or until a toothpick inserted comes out clean.

Allow the muffins to cool in the muffin pan for 5 minutes, then transfer to a wire rack to continue cooling.

Muffins stay fresh covered at room temperature for a few days, then transfer to the fridge for up to 1 week.