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