Place 1 cup of the rolled oats and 1 cup milk in a large bowl and stir to combine. Let sit for 20 minutes.

Meanwhile, arrange a rack in the middle of the oven and heat the oven to 400ºF. Line a standard 12-well muffin tin with paper liners or coat with cooking spray.

In a medium bowl, whisk together 1 ½ cups all-purpose flour, ½ cup packed brown sugar, 1 teaspoon ground cinnamon, 1 teaspoon baking powder, and ½ teaspoon baking soda.

Melt 1 stick unsalted butter if using. Add the butter or ½ cup vegetable or canola oil, egg, vanilla extract, and kosher salt to the oat mixture and whisk until combined.

Add the flour mixture and fold until almost combined with a few streaks of flour left. Scatter blueberries and fold until evenly distributed.

Divide the batter among the muffin wells, sprinkle with the remaining oats.

Bake until golden brown and a tester comes out clean, 20 to 22 minutes.

Let cool for 5 minutes in the pan. If not using liners, run a knife around each muffin to loosen. Transfer to a wire rack and cool for at least 15 minutes.