Preheat oven to 375 degrees. Line a baking sheet with parchment paper.

Whisk together the flour, cocoa, baking soda, and salt in a medium bowl; set aside.

With a hand mixer, beat the melted butter, white sugar, and brown sugar in a large bowl until combined.

Add the mashed banana and mix until combined.

Add the egg yolk and vanilla and beat until creamy and smooth.

Add the dry ingredients and mix with a rubber spatula until combined–don’t overmix.

Stir in most of the chocolate chips.

Use a cookie scoop or spoon to scoop the dough into balls, about 2 tablespoons of dough per cookie.

Roll into a ball and place on the prepared baking sheet, about 2 inches apart.

Gently flatten the tops of the cookies with the palm of your hand.

Place the cookies in the oven and bake for 8-10 minutes or until set but still soft in the center.

Remove from the oven and immediately press a few chocolate chips onto the tops of each cookie and sprinkle them with flaky sea salt.

Let the cookies cool on the baking sheet for about 5 minutes and then transfer them to a cooling rack to cool completely. Serve with ice-cold milk (if desired) and enjoy.