In large bowl, beat 1/2 cup butter and 1 1/2 cups granulated sugar with electric mixer on high speed about 2 minutes. Beat in mashed bananas and 1 teaspoon vanilla. Beat 30 seconds. Add eggs; beat on high speed 1 minute, scraping sides of bowl frequently. On low speed, add flour mixture, about one-third at a time, and sour cream, about half at a time, beating just until combined. Stir in cooled coffee mixture.