Start by preheating your oven to 375°F. While the oven heats up, find a 2-quart baking dish or an 8×8 inch square pan. Grease the inside of the dish with a little bit of butter or a light spray of oil.
In a large mixing bowl, stir together the rolled oats, brown sugar, baking powder, cinnamon, and salt. Use a whisk to make sure the baking powder and cinnamon are spread evenly through the oats. If you are adding walnuts or pecans for a bit of crunch, toss half of them into this dry mix now.
In a separate medium-sized bowl, beat the egg until the yolk and white are fully combined. Stir in the milk, melted butter, and vanilla extract. Whisk these together until the mixture is a uniform color.
Spread about half of your blueberries across the bottom of the greased baking dish. If you are using frozen berries, there is no need to thaw them first; just toss them right in.
Pour the dry oat mixture over the layer of berries in the dish. Use a spoon to level out the oats so they form an even layer. You don’t need to press them down firmly; just make sure they are spread out to the corners of the pan.
Slowly pour the wet egg and milk mixture over the top of the oats. You want to pour it gently so you don’t disturb the layers too much. Give the pan a very light shake to help the liquid seep down into all the gaps between the oat grains.
prinkle the remaining blueberries and the rest of the chopped nuts over the surface for a nice presentation.
Slide the dish into the center of your oven and bake for 35 to 40 minutes. Once you pull the dish out of the oven, let it sit on the counter for about five to ten minutes. before serving.
