Preheat oven at 350oF
Beat butter, softened, at medium speed with an electric mixer until creamy; gradually add sugar, beating well.
Add eggs, banana mashed and vanilla, beating until blended.
Add flour to banana mixture alternately with buttermilk, beginning and ending with flour; beat at low speed until blended after each addition.
Place paper baking cups in muffin pans, and coat with cooking spray; spoon batter into pans, filling cups two-thirds full..
Bake for 17 minutes. Remove cupcakes from pans immediately, and cool on wire racks. Spread with frosting, if desired.
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