Combine flour, baking powder, baking soda and salt. Beat butter and sugar in large bowl with mixer until blended.
Add bananas, sour cream and eggs; mix well.
Add flour mixture; mix just until moistened. Stir in nuts.
Pour into greased and floured 9x5-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.
Cook chocolate and cream in small saucepan on low heat 3 to 5 min. or until chocolate is completely melted, stirring frequently. Cool 5 min. or until slightly thickened.