Preheat the oven to 350℉. Line two baking trays with parchment paper and set aside.
Brown the butter: In a medium sized saucepan, add the butter and melt it on medium heat. Once it melts, it will crackle, then become foamy – continue stirring the butter to prevent burning. The butter will then go from melted to golden brown within a few minutes, and you'll know it's almost done when the aroma of browned butter arrives and you see golden specks on the bottom of your pot. The whole process should take about 5 minutes! Once golden, remove from heat and transfer to a glass bowl to cool for 20 minutes while you prep the rest of the ingredients.
1/2 cup + 2 tbsp butter unsalted butter
In a medium bowl, add in all-purpose flour, cinnamon, baking soda, baking powder, cornstarch, and salt.
2 cups all-purpose flour, 1 tbsp cornstarch, 1 tsp baking soda, 1/4 tsp baking powder, 1/2 tsp cinnamon, 1/4 tsp salt
In a large bowl, add in slightly cooled brown butter, brown sugar, and white sugar. Whisk together until well combined. Then mix in egg, egg yolk, vanilla, and mashed bananas.
1/2 cup mashed bananas, 1/2 cup + 2 tbsp butter unsalted butter, 1/2 cup dark brown sugar, 1/4 white sugar, 1 tbsp vanilla, 1 large egg*, 1 large egg yolk
Add the dry into the wet. Using a spatula, mix until a soft cookie dough forms. Don't over-mix! If your batter is runny, allow it to sit on your counter for 5-10 minutes. This will allow the flour to hydrate and thicken the cookie dough before scooping.
Add in the chocolate chips and mix a few more times.
3/4 cups semi-sweet chocolate chips
Scoop the cookies (About 2 tbsp of cookie dough at a time) onto the prepared baking tray placing them about 2 inches apart from one another. Gently flatten the cookies before baking as they do not spread a lot. Bake 6 at a time for 14-16 minutes or until the edges are a light golden brown. The middle may look soft and underbaked, but it will continue to bake as it sits on the hot tray.
Store these cookies on your counter for a day, in an airtight container for up to 3 days, or in the fridge for a week. You can also freeze the cookies and thaw in the microwave if you like.