Preheat oven to 375 degrees. Prepare muffin pan with cooking spray or muffin liners. Set aside.
Whisk together flour, baking powder, baking soda and salt in a medium-sized bowl.
Cream together the oil and brown sugar. Add the peanut butter and mix until incorporated. Beat in the vanilla and eggs, one at a time. Scrape sides of the bowl often to make sure everything is evenly mixed.
Add one-third of the dry ingredients and mix until moistened. Add half of the buttermilk, mix until combined. Add the remaining dry ingredients and remaining buttermilk. Fold in chocolate chips, if using.
Divide batter evenly between prepared muffin pan. Sprinkle with chopped peanuts, if using. Bake until golden brown, 22-24 minutes. Remove from oven and allow to cool in pan for 5 minutes, then move to wire rack to cool completely.
Recipe by Alida's Kitchen at https://www.alidaskitchen.com/2011/07/20/whole-wheat-peanut-butter-muffins/