1. Combine flour, baking powder and baking soda. 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.
2. Pour into greased and floured 9x5-inch loaf pan.
3. Bake 1 hour or until toothpick inserted in centre comes out clean. Cool 5 min. Remove from pan to wire rack; cool completely.
4. 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. Drizzle over bread; let stand until firm.