1Heat oven to 350°F. Grease bottom only of 9x5-inch or 8x4-inch loaf pan with shortening.
2In large bowl, beat cake mix, mashed bananas, butter and eggs with electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally. Pour into pan.
3Bake 9-inch loaf 55 to 60 minutes, 8-inch loaf 1 hour 5 minutes to 1 hour 15 minutes, or until toothpick inserted in center comes out clean. (Place sheet of foil over loaf to prevent overbrowning.) Cool 10 minutes. Loosen sides of loaf from pan; remove from pan to cooling rack. Cool about 1 hour before slicing.