Recipe: Peanut Peanut-Butter Muffins

This recipe is wonderful. It comes from a book titled "Muffins A to Z" by Marie Simmons. I've mad many of the muffins from this book and have never found one we haven't loved.
Peanut Peanut-Butter Muffins
1/2 cup smooth peanut butter 1 1/2 tsp. baking soda,sieved
3/4 cup packed light brown sugar 1/2 tsp. salt
2 large eggs 1 1/2 cups buttermilk
1 tsp vanilla extract 1/2 cup chopped dry-roasted
2 1/2 cups all purpose flour unsalted peanuts

1. Preheat oven to 400 degrees F. Lightly butter 12 muffin cups or coat with nonstick cooking spray.
2. With a mixer, beat the peanut butter and brown sugar together in a large bowl until well blended. Beat in the eggs, one at a time, beating well after each addition. Beat in the vanilla.
3. In a large bowl, combine the flour, baking soda and salt; stir until blended. Fold the dry ingredients and the buttermilk alternately into the peanut butter mixture, beginning and ending with the dry ingredients. Do not overmix.
4. Divide the batter evenly among the muffin cups. Sprinkle each muffin with 1 heaping teaspoon of the chopped peanuts.
5. Bake until a toothpick inserted in the centers comes out clean, 20 to 22 minutes. Cool on a wire rack before removing from the pan.