Heat oven to 350ºF.
Beat butter and sugar in large bowl with mixer until blended. Add eggs and sour cream; mix well. Add bananas and combined dry ingredients; mix just until moistened. Stir in nuts.
Pour into greased and floured 9×5-inch loaf pan.
Bake 1 hour or until toothpick inserted in center comes out clean. Cool 5 min.; remove from pan to wire rack. Cool completely before slicing. Refrigerate leftovers.