Prepare the Dough:
In a large bowl, combine the melted butter (or vegetable oil), packed brown sugar, and mashed banana. Mix until fully combined.
Add the egg yolk and vanilla extract, mixing well to ensure the ingredients are fully incorporated.
Mix the Dry Ingredients:
Add the flour, baking soda, cinnamon, and salt to the wet mixture. Stir until everything is combined and no streaks of flour remain.
Fold in the Chocolate Chips:
Gently fold the chocolate chips into the dough. Set the dough aside to allow the flour to hydrate while you preheat the oven.
Preheat the Oven and Prepare the Baking Sheet:
Preheat your oven to 350°F (175°C) and line a cookie sheet with parchment paper.
Shape and Bake the Cookies:
Once the oven is preheated, use a cookie scoop or a spoon to portion out the dough into 1-inch balls. Roll the dough into smooth balls with your hands and place them 2 inches apart on the prepared cookie sheet.
Bake for 10 to 11 minutes, or until the edges of the cookies are set and the centers are puffed but still slightly underbaked.
Cool and Enjoy:
Allow the cookies to cool on the baking sheet before transferring them to a wire rack. Enjoy these soft, chewy, banana-flavored cookies with gooey chocolate chips!