Preheat your oven to 350°F (175°C) and prepare a 9-inch round cake pan by greasing and flouring it.

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt; set aside.

In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy, about 3-5 minutes.

Add the eggs one at a time, beating well after each addition. Mix in the mashed bananas, followed by the buttermilk and vanilla extract.

Gradually add the dry ingredients to the wet mixture, stirring gently until just combined.

Pour the batter into the prepared cake pan and bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.

Let the cake cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.

In a saucepan over medium heat, melt the butter for the caramel sauce. Stir in the brown sugar and heavy cream, bringing to a gentle simmer.

Stir constantly for 5 minutes or until the sauce thickens, then remove from heat and stir in the vanilla extract and a pinch of salt.

Once the cake has cooled, drizzle the caramel sauce over the top, letting it cascade down the sides.

Garnish with toasted walnuts and freshly sliced bananas.