In a sauce pan or pot, melt the butter on low heat until the butter to begins to foam. Once it starts to foam, whisk or stir the liquid butter frequently. The butter will begin to smell nutty and very fragrant. Once the foam has subsided, the butter should have some brown, lightly toasted bits floating at the bottom. Pour the brown butter in a heat safe bowl to cool for about 15 - 20 minutes to room temperature. 10 tablespoons (141 g) unsalted butter
In another bowl whisk together the flour, baking soda, ground cinnamon and salt until well combined.
1½ cups (180 g) all purpose flour, 1 teaspoon ground cinnamon , ½ teaspoon baking soda, ½ teaspoon salt
In a large mixing bowl, whisk in the cooled browned butter with the light brown and granulated sugars until well combined. Whisk in the mashed banana, egg yolk and vanilla extract until smooth and well combined.
½ cup (100 g) light brown sugar, ¼ cup (50 g) granulated sugar, ½ cup (118 ml) mashed banana (about 1 large ripe banana), 1 large egg yolk (US), room temperature, 1 teaspoon (5 ml) vanilla extract
Stir the dry ingredients into the wet until just combined. I like to do this about ½ of the dry ingredients at a time. Fold in most of the chocolate chips. Reserve about ½ cup (85 g) for topping the cookies right before baking.
1¼ cup (212 g) chocolate chips, divided
Cover the cookies with plastic wrap and transfer to the fridge to chill for 1 hour or up to overnight. 30 minutes before baking the cookies, preheat the oven to 350 F (177 C). Line a large baking sheet with parchment paper. Using a medium cookie scoop (2 tablespoons, 30 ml), scoop the chocolate chip banana cookie dough and place the cookie dough balls onto the lined baking sheet about 3 inches (8 cm) apart. Top with the reserved chocolate chips. Bake for 10 - 12 minutes or until the edges of the cookies are set and the centers are slightly puffed. Cool the chewy chocolate chip cookies with banana on the baking sheet for 5 minutes. Top with a sprinkle of flaky salt if you like. Then transfer to a cooling rack to cool completely to room temperature and enjoy!
1 tablespoon flaky salt for topping, optional to taste