1. Beat butter or margarine until fluffy in large bowl of electric mixer at high speed. Gradually add sugar; continue beating until light and fluffy. Beat in eggs, 1 at a time. Add vanilla.
2. Sift flour, baking powder, baking soda and salt onto wax paper. Add to sugar mixture alternately with sour cream. Add banana and pecans; mix just until blended. Turn into a greased and floured 13x9x2-inch baking pan.
3. Bake in moderate oven (350°) 40 minutes, or until center springs back when lightly pressed with fingertip. Cool cake in pan 10 minutes. Turn out onto wire .rack; cool completely. Frost with praline topping. Broil, 3 inches from heat, 3 minutes.