Preheat oven to 350 degrees. Line 24 muffin cups with paper-liners.
Beat butter and cream cheese at medium speed with an electric mixer until creamy. Gradually add sugar, beating until light and fluffy. Add eggs, 1 at a time, beating just until blended after each addition.
Combine flour and next 3 ingredients, gradually add to butter mixture, beating at low speed until just blended. Stir in bananas, pecans, and vanilla. Spoon batter into prepared muffin cups.