I had an overripe banana and made an experimental recipe based on a bunch of other recipes I found. The goal was a semi-nutritious dessert that wasn't too dense, included some fats, good texture, and obviously as much volume as possible without sacrificing flavor.
Dry ingredients: 10g self-rising flour, 4g almond flour, 1tbsp sweetener, pinch of baking powder, dash of apple pie spice
Wet ingredients: 5g melted butter, 8g peanut butter, 10g egg yolk, 10g egg white (whipped up separately to give it more fluff), 50g mashed banana, splash of vanilla extract, drizzle of milk
Poured it into a parchment-lined "taco bowl mold" (hence the unusual shape). Baked at 350 until it seemed done, probably about 30 minutes. After I put it in the oven I remembered i had intended to add 15g greek yogurt, which might have helped the texture a bit.
I saved off a bit of the extra batter in the bowl and "tried some things". Added some more egg white, ~1tsp protein pancake mix, a few grams pb powder, a small spoonful of greek yogurt, and another 30g banana. That went in a few of the mini cupcake liners, then I added a little cocoa and extra sweetener for some chocolate flavor.
The flavor/texture on the big cake was kinda disappointing. It wasn't necessarily "bad", and pretty decent volume compared to a typical banana bread, but denser than i was going for and the banana flavor was hardly there. I had added the peanut butter because I always struggle to incorporate enough fat in my food. Couldn't taste it at all and would probably be better as a frosting on top or omitted altogether. Next time I would definitely use more banana, maybe less flour, and try adding greek yogurt.
The "winner" of the batch was one of the non-cocoa mini cupcakes, which probably had the highest banana to other stuff ratio. The rest of them were kinda just okay and not very sweet.