Prepare the Cake Batter: Preheat oven to 350°F (175°C). Grease a 9-inch round cake pan. In a bowl, whisk together flour, baking soda, baking powder, salt, and cinnamon. In another bowl, beat butter, granulated sugar, and brown sugar until fluffy. Add eggs and vanilla, mixing well. Stir in mashed bananas and sour cream. Gradually add dry ingredients and mix until combined. Fold in chopped pecans.

Bake the Cake: Pour batter into the prepared cake pan. Bake for 35-40 minutes, until a toothpick inserted in the center comes out clean. Let cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

Make the Caramel Sauce: In a saucepan over medium heat, melt butter and stir in brown sugar. Cook for 2 minutes, then slowly add heavy cream, stirring constantly. Simmer for 3-4 minutes until thickened. Remove from heat, stir in salt and vanilla, and let cool slightly.

Assemble the Cake: Pour warm caramel sauce over the cooled cake. Sprinkle with toasted pecans.

Serve: Slice and enjoy warm or at room temperature.