Preheat oven to 375F (190C). Lightly spray or grease 12 muffin tins.
In a small saucepan melt butter over medium heat. Whisk in peanut butter. Pour into a large bowl to cool.
In a medium bowl, place flours, baking powder, cinnamon and baking soda. Whisk together ensuring there are no lumps.
Stir sugar into cooled peanut butter mixture. Then stir in eggs until completely blended. Stir in bananas and vanilla. Gradually add flour mixture, stirring just until combined.
Spoon into muffin tins. Sprinkle with peanuts, gently pushing into batter. Bake in centre of preheated oven until golden and a skewer inserted in centre comes out clean, 16 to 18 minutes. Remove muffins from pan to a rack to cool.
Nutrients per muffin: 335 calories, 15 g total fat (6 g saturated fat, 0.4 g trans fat, 3 g monounsaturated fat, 1 g polyunsaturated fat), 51 mg cholesterol, 8 g protein, 45 g carbohydrates, 3 g fibre, 16 g sugars, 128 mg sodium, 160 mg potassium, 18 mg calcium (2 % DV), 2 mg iron (14 % DV).