Preheat your oven to 350°F (175°C) and toast the pecans on a baking sheet for 8-10 minutes.

In a saucepan, combine 1/4 cup butter and 1/2 cup brown sugar. Cook until smooth and bubbling, then thicken slightly and let cool.

Mix chopped and whole pecans into the caramel sauce and set aside.

Mash the bananas in a bowl. In another bowl, combine flour, baking powder, baking soda, and salt. In a third bowl, cream butter and sugar, then add eggs, vanilla, and mashed bananas.

Alternate adding the dry ingredients and buttermilk to the banana mixture until just blended.

Grease and flour a 9x13-inch pan. Layer half of the batter, then half of the topping, followed by the remaining batter and topping.

Bake for 45-55 minutes, checking for doneness with a skewer. Cool in the pan for 15-20 minutes.