01 - Preheat oven to 350°F. Grease and flour a 9x13-inch cake pan or line it with parchment paper.
02 - In a medium bowl, whisk together the flour, baking powder, baking soda, and salt until evenly distributed.
03 - In a large bowl, beat the granulated sugar with vegetable oil or melted butter until well combined and smooth.
04 - Add the eggs one at a time, mixing thoroughly after each addition. Stir in the vanilla extract.
05 - Gently fold in the mashed bananas and buttermilk (or yogurt) until just combined.
06 - Add the dry ingredient mixture to the wet ingredients, folding gently until no flour streaks remain. Take care not to overmix.
07 - If desired, fold in the chopped walnuts, pecans, or chocolate chips until evenly distributed throughout the batter.
08 - Pour the batter into the prepared cake pan, using a spatula to smooth the top evenly.
09 - Bake for 35–40 minutes, or until a toothpick inserted into the center comes out clean.
10 - Let the cake cool in the pan for 15 minutes, then turn it out onto a wire rack to cool completely. Serve plain or topped with your favorite frosting.