Preheat your oven to 350°F (175°C). Grease and flour a 9x13-inch baking pan.
In a medium bowl, whisk together the flour, baking soda, and salt. Set aside.
In a large mixing bowl, cream the butter, granulated sugar, and brown sugar until light and fluffy.
Beat in the eggs one at a time, then add the vanilla extract and mashed bananas.
Gradually mix in the flour mixture, alternating with the buttermilk, until well combined.
Fold in the chopped pecans and pour the batter into the prepared pan.
Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean. Allow the cake to cool completely in the pan.