Preheat oven to 350F/180C. Butter a 9×5-inch loaf pan.

Make the banana topping: Melt butter in a small deep heavy saucepan over medium heat. Once it starts to bubble, add sugar and let simmer for 3 minutes until thick and smooth. Pour into prepared pan.

Cut bananas in half lengthwise and, depending on the size of the bananas and pan, cut each half into 2 or 3 pieces widthwise. Place bananas over caramel, cut side down.

In a medium bowl, sift together flour, baking powder, baking soda, and salt. Set aside.

In a standing mixer fitted with the paddle attachment, beat together butter and sugar for 2-3 minutes until light and fluffy. Occasionally scrape down the sides and bottom of the bowl. On medium speed, add eggs one at a time, beating well after each addition. Beat in vanilla extract. On low speed, beat in the flour mixture in 3 additions, alternating it with the sour cream in 2 additions, starting and ending with the flour. Do not over mix.

Pour batter carefully into pan over bananas and smooth the top. Bake for 40 – 50 minutes or until golden and a skewer inserted into the center of the cake comes out clean. Let the cake cool for exactly 5 minutes on a wire rack, then invert it onto a plate and let cool completely.

Serve warm or at room temperature. Store cake in the refrigerator for up to 3 days.