In a small bowl, soak the oats in the cup of milk for at least 20-30 minutes before using. This lets the oats soak up the moisture and make them soft for the insides of the muffins.
Preheat the oven to 425℉/220℃/Gas Mark 7.
In a large bowl, whisk together the all-purpose flour, baking powder, baking soda, cinnamon, and salt together.
In a medium bowl, add the melted butter, brown sugar, egg, and vanilla extract. Whisk together, then begin to pour the wet ingredients into the dry ingredients. Stir them together until they are just incorporated.
Pour in the milk and oats and blueberries into the bowl and fold into the batter.
Pour the blueberry oat batter into the greased or lined muffin tins. Fill the muffin tins to the top. Place into the oven and bake at the high heat for 5 minutes.
With the muffins still in the oven, reduce the heat to 350℉/175℃/Gas Mark 4 and continue to bake for 13-15 minutes or until a toothpick inserted into the muffins comes out clean. Remove from the oven and let cool in the muffin tray for about 5 minutes.
Remove the muffins from the muffin tray and continue to let cool on a cooling rack. Serve and enjoy!