So I tried many different variations: More and less flour, banana, and yogurt; different combinations of baking powder and soda; different amounts of butter. I stopped short of experimenting with types of flour or mixing methods, because I wanted to keep the instructions simple and the ingredients, basic pantry items. But I kept hitting up against a wall: Delicious banana flavor, but gummy, dense texture. And then, as I was pulling out my baking pans to try yet another variation, I realized the problem. I'd been stuck on the idea that banana bread had to be in a loaf shape. No wonder the low fat version was heavy and gummy in the middle. It wasn't getting enough heat at its center. A good banana bread is moist and sweet like a cake anyway, and I decided that shape was much less important than good texture. So I scrapped the 8"x4"x3" loaf pan for a 10"x2" round cake pan. Result: Shorter cooking time, 30-40 minutes instead of 60-70. Lighter color than a traditional banana bread, but prominent banana flavor. A moist, light and tender crumb. And only two tablespoons of butter (22 grams of fat) in the whole thing.
You will need:
1 1/2 cups very ripe bananas, about 4 medium bananas. They should be very soft, covered with brown spots, and falling away from their stems. The more ripe and soft they are, the moister your cake, and the reason why this recipe doesn't need a lot of butter. Mash by hand in a large bowl with a potato masher until smooth.
3/4 cup sugar
2 eggs, lightly beaten (I used jumbo, but you can use large or extra large as well. The texture and height of your cake may be slightly different with smaller eggs, but this recipe is pretty forgiving.)
1/4 cup plain low fat (2%) yogurt
2 tablespoons unsalted butter, melted and cooled, plus a little more for greasing the pan
1 teaspoon real vanilla extract
2 cups unbleached all purpose flour, plus a little more for flouring the pan
1 teaspoon baking soda
1/2 teaspoon salt
1/2 cup chopped walnuts, optional (I don't use them because some people don't like nuts, and I can't eat a whole cake myself, and I like the smooth texture of the plain cake. But by all means, if you like them, use them.
Preheat oven to 350 degrees and adjust the oven rack to the bottom middle position. Butter and flour the bottom of a round or square cake pan (8"x8" square, 9" or 10" round, whatever you have. Just make sure it's at least 2" high, and I prefer plain aluminum rather than non-stick - they last longer because there's no non-stick finish to degrade at high temperatures, and you can control sticking by properly greasing the pan or using parchment paper.)
In a large bowl, mix together the mashed bananas, sugar, eggs, yogurt, butter, and vanilla. In a separate bowl, sift together the flour, baking soda, salt, and nuts if you're using them, and mix well. Add the dry ingredients into the wet, and stir gently with a wooden spoon until just mixed and you no longer have large patches of dry flour. A couple of streaks of flour are fine. Do not over mix or the gluten in the flour will develop and your cake will be tough. Using a rubber spatula, scrape the cake batter into the prepared pan, make sure the batter is evenly distributed (it's a pretty thick batter) and place in the oven.
Bake for 30-40 minutes, until a sharp knife or toothpick inserted into the center of the cake comes out clean. Run a knife around the outside of the cake to release the edges from the pan, then leave the cake to cool in the pan for 5 minutes. Then turn the cake onto a plate. It should come out cleanly and be bottom-side-up. Now flip the cake again onto a cooling rack. It will be right-side-up. Serve warm or at room temperature. Nothing is better for breakfast.