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 sugar and oil (or melted butter) together until well combined. Add the eggs one at a time, mixing thoroughly after each addition. Stir in the vanilla extract.
04 - Fold the mashed bananas and buttermilk (or yogurt) into the wet mixture until just combined.
05 - Gradually add the dry ingredients to the wet mixture, folding gently just until no flour spots remain. Be careful not to overmix.
06 - If using, gently fold the chopped nuts or chocolate chips into the batter.
07 - Pour the batter into the prepared cake pan, smoothing the top with a spatula for an even layer.
08 - Bake for 35–40 minutes, or until a toothpick inserted into the center comes out clean.
09 - Let the cake cool in the pan for 15 minutes, then turn it out onto a wire rack to cool completely. Serve plain or with your favorite frosting.