Heat the oven to 350°F (177°C) and lightly grease a 10-ounce ramekin. In a small bowl, combine flour, baking soda, cinnamon, and salt together. Set aside.
Mash the banana with a fork and add to a medium-sized bowl. Add the sugar and with an electric mixer or a wire whisk whip the banana and sugar together.
Add the melted butter, the egg yolk, and the vanilla; mix well.
Add the dry ingredients and mix until combined.
Pour into the ramekin and bake for 25-30 minutes until golden brown.
Remove from the oven and cool slightly before eating.
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Notes
Use A Very Ripe Banana: Brown-spotted bananas provide the best flavor and moisture.
Do Not Overmix: Stir only until the flour disappears to keep the bread tender.
Leave Some Texture: A few small banana pieces add to the overall texture.
Check for Doneness: A toothpick inserted in the center should come out with a few moist crumbs.