Whisk peanut butter, maple syrup and brown sugar until glossy. Whisk in the egg and vanilla until no streaks remain.
In a separate bowl, whisk oat flour, baking soda, fine salt and optional cinnamon, breaking up all soda clumps.
Fold dry ingredients into the peanut butter mixture just until no flour remains. Fold in optional chopped peanuts.
Cover and refrigerate for 30 minutes. The dough should hold a soft mound; adjust only after chilling if needed.
Heat the oven to 350°F with a center rack and line two light-colored sheet pans with parchment.
Divide into 16 portions of about 31 grams. Roll gently, place 2 inches apart and crosshatch with a fork to 1/2 inch thick.
Bake one pan at a time for 9 to 12 minutes, until the edges are dry and lightly browned while the centers remain soft and matte.
Leave cookies undisturbed on the pan for 10 minutes, then transfer with a thin spatula to a rack and cool completely.
