In a large mixing bowl, combine 1/4 cup of mashed overripe banana with 1/2 cup of melted butter or vegetable oil and 3/4 cup of light brown sugar. Mix until smooth, about 1-2 minutes.

Add 1 egg yolk and 1 teaspoon of vanilla extract to the banana mixture. Stir until combined.

Gradually add 1 cup of all-purpose flour, 1/2 teaspoon of baking soda, 1/4 teaspoon of ground cinnamon, and a pinch of salt to the wet mixture. Fold gently until no dry flour is visible.

Fold in 1/2 cup of chocolate chips and let the batter rest for about 15 minutes.

Preheat your oven to 350°F (175°C) while the batter rests. Line a cookie sheet with parchment paper.

Using a cookie scoop, portion out 1-inch balls of dough and place them on the prepared cookie sheet, spacing about 2 inches apart.

Bake the cookies for 10-11 minutes. The edges should be set, but the centers may look undercooked.

Cool the cookies on the baking sheet for about 5 minutes before transferring them to a wire rack.