Preheat your oven to 350°F (175°C) and prepare three 9-inch round cake pans by greasing and flouring them.

In a mixing bowl, whisk together the flour, baking powder, baking soda, and salt. In another bowl, cream the butter with granulated and brown sugars until light and fluffy.

Add the eggs one at a time, blending well after each addition. Then, mix in the vanilla and mashed bananas.

Gradually add the dry ingredients to the wet mixture, alternating with buttermilk. Fold in the chopped pecans.

Divide the batter evenly among the prepared pans and bake for 25-30 minutes, checking for doneness with a toothpick.

Let the cakes cool in the pans for 10 minutes before transferring to wire racks to cool completely.

Melt butter in a saucepan, add brown sugar and heavy cream, bring to a gentle boil while whisking. Remove from heat and mix in powdered sugar.

Once the cakes are cool, assemble by placing one layer on a plate, spread frosting on top, and repeat with remaining layers. Frost the sides and top, garnishing with chopped pecans.

Let the cake sit for at least 30 minutes before serving to allow flavors to meld.