Add the melted butter, packed brown sugar, and 1/4 cup mashed banana to a large mixing bowl. Stir until thoroughly combined.

Add the egg yolk and vanilla extract. Mix until smooth and incorporated.

Add the all-purpose flour, baking soda, cinnamon, and salt.

Gently stir the dry ingredients into the wet mixture just until combined and no visible streaks of flour remain. Avoid overmixing.

Fold the chocolate chips evenly throughout the cookie dough.

Cover the bowl and allow the dough to rest at room temperature for about 15 minutes. This gives the flour time to hydrate while you preheat the oven.

Preheat the oven to 350°F (175°C). Line a large baking sheet with parchment paper.

Using a 1-ounce cookie scoop or spoon, portion the Banana Bread Chocolate Chip Cookies dough onto the prepared baking sheet. Leave approximately 2 inches between each cookie. The dough will be softer and wetter than traditional chocolate chip cookie dough.

Bake for 10–11 minutes, or until the edges look set and the cookies have puffed slightly. The centers should still appear a little underbaked when removed from the oven.

Let the cookies cool on the baking sheet for several minutes before transferring them to a wire rack. Cool before serving so the soft centers have time to set