Preheat oven to 350° F with the rack in the middle. Combine the flour, sugar, baking powder, salt and cinnamon in a large mixing bowl.

Add the peanut butter to the flour mixture, blending it in with a fork until you have a coarse, crumbly texture. Stir in the milk, egg, butter and vanilla. Fold in the peanut butter chips.

Coat a nonstick muffin pan with cooking spray. Fill each muffin cup about 3/4 full with batter.

Bake for 15 to 20 minutes or until the muffins are light golden brown. Cool on a wire rack.