Banana Nut Cake with Cream Cheese Frosting

For the Cake:
- 3 ripe bananas, mashed
- 2 cups all-purpose flour
- 1 1/2 teaspoons baking powder
- 1/2 teaspoon baking soda
- 1/4 teaspoon salt
- 1/2 cup unsalted butter, softened
- 1 cup granulated sugar
- 1/2 cup brown sugar
- 2 large eggs
- 1 teaspoon vanilla extract
- 1/2 cup buttermilk
- 1 cup chopped walnuts or pecans
For the Frosting:
- 8 oz cream cheese, softened
- 1/2 cup unsalted butter, softened
- 3-4 cups powdered sugar, sifted
- 1 teaspoon vanilla extract
For Topping:
- Sliced bananas
- Whole pecans or walnuts
- Caramel sauce for drizzling