1 Heat oven to 325°F. Generously spray 10- or 12-cup fluted tube cake pan.
2 In large microwavable bowl, mix butter, brown sugar and bananas. Microwave uncovered on High 1 minute 40 seconds to 2 minutes or until bananas are cooked and caramelized.
3 Add cake mix, sour cream, vegetable oil and eggs. Beat with electric mixer on low speed 1 minute. Increase speed to medium; beat 2 minutes. Stir in walnuts. Pour into pan.
4 Bake 40 to 45 minutes or until toothpick inserted in center comes out clean. Cool 15 minutes; turn upside down onto cooling rack or heatproof serving plate, and remove pan. Cool completely, about 1 hour. Place cake on serving plate.
5 Drizzle cake with caramel topping. Sprinkle with kosher salt.