In a large mixing bowl, stir together 1 1/2 cups white whole wheat flour, rolled oats, brown sugar, Baking powder, cinnamon, and salt. In a separate bowl, whisk together the milk, butter, eggs, and vanilla. Make a well in the center of the dry ingredients, add the wet ingredients to the well, then carefully stir by hand, just until blended.
Place a rack in the center of your oven and preheat to 400 degrees F. Lightly coat a standard muffin tin with cooking spray or line with paper liners, then coat the liners with cooking spray. Set aside.