Preheat your oven to 350 degrees Fahrenheit (175 degrees Celsius). Line two large baking sheets with parchment paper.

In a large bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.

Add the mashed bananas, egg yolk, and vanilla extract to the butter mixture. Stir until well combined.

In a separate bowl, whisk together the flour, baking soda, salt, and cinnamon.

Gradually add the dry ingredients to the wet ingredients, mixing just until combined. Fold in the chocolate chips if using.

Use a cookie scoop to drop rounded tablespoons of dough onto the prepared baking sheets, leaving about two inches of space between each cookie.

Bake for 10 to 12 minutes, or until the edges are lightly golden. Allow the cookies to cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely.