Preheat the oven to 350°F (177°C) and lightly grease a 10-ounce ramekin.
In a small bowl, whisk together the flour, baking soda, cinnamon, and salt. Set aside.
In a medium bowl, mash the banana with a fork. Add the sugar and beat with a whisk or mixer until well combined.
Mix in the melted butter, egg yolk, and vanilla.
Stir in the dry ingredients until just combined, then fold in the chocolate chips.
Pour the batter into the prepared ramekin. Place the ramekin on a rimmed baking sheet.
Bake for 25–30 minutes, or until the top is golden and a toothpick inserted in the center comes out clean. Let cool for a few minutes before serving.
Notes
Use a Ripe Banana: Choose a banana with brown spots for the sweetest flavor and easy mashing.
Measure Flour Correctly: Spoon flour into the measuring cup and level it off. Don’t pack it down.
Grease the Ramekin: Coat well so the bread releases easily after baking.
Check for Doneness: Bake 25–30 minutes, but ovens vary. Insert a toothpick into the center - if it comes out clean or with a few moist crumbs, it’s ready.