Preheat oven to 350°F (180°C). Grease and flour an 8-inch round cake pan.
In a medium bowl, whisk together flour, baking powder, baking soda, and salt.
In a large bowl, beat the butter and sugar until creamy. Add eggs one at a time, beating well after each. Mix in vanilla extract.
Stir in mashed bananas and sour cream until combined.
Gradually add dry ingredients to the wet mixture and stir until just combined. Fold in chopped pecans.
Pour batter into prepared pan and smooth the top. Bake for 45–50 minutes or until a toothpick inserted in the center comes out clean.
Let the cake cool completely. Prepare the caramel sauce.