Spread the oats into a single layer on a half sheet pan. Bake until lightly toasted, about 20 minutes. Cool the oats in the pan for 2 to 3 minutes.
Grind 8 ounces of the toasted oats in a food processor until the consistency of whole-wheat flour, about 3 minutes.
Add the baking powder, cinnamon, and salt to the food processor and pulse 2 to 3 times to combine. Set aside.
Combine the butter and sugars in the bowl of a stand mixer, and mix on medium speed using the paddle attachment until light in color about 3 minutes. Stop once to scrape down the sides of the bowl. Reduce mixer speed to the lowest speed and add the egg and vanilla extract. Mix to combine.
Slowly add the flour mixture until just combined. Stop once to scrape down the sides of the bowl. Add the remaining toasted oats and the raisins. Stir to combine.
Scoop the dough with a 1 1/2-ounce disher or server onto parchment-lined half sheet pans, leaving 2 inches between each mound. Bake until the cookies begin to brown around the edges, about 12 to 14 minutes. Rotate the pan halfway through the cooking time. Cool the cookies on the pans for 2 minutes, then remove them to a cooling rack to cool completely.
Note: based on an Alton Brown recipe.
There are 144 calories in 1 serving of Oatiest Oatmeal Cookies.