In the bowl of a stand mixer fitted with the paddle attachment, or in a large mixing bowl using a handheld mixer, beat the butter, brown sugar, and granulated sugar together for 1 to 2 minutes or until well combined.
¾ cup unsalted butter, ¾ cup packed light brown sugar, ½ cup granulated sugar
Mix in the mashed banana, egg yolk, and vanilla extract until fully combined, stopping to scrape down the sides of the bowl as needed.
½ cup mashed ripe banana, 1 large egg yolk, 1 ½ teaspoons pure vanilla extract
In a separate large mixing bowl, whisk together the flour, cornstarch, baking soda, baking powder, and salt.
2 ½ cups all-purpose flour, 1 tablespoon cornstarch or cornflour, ½ teaspoon baking soda, ½ teaspoon baking powder, ¼ teaspoon salt
Add the dry ingredients to the wet ingredients and mix until just combined, then mix in the chocolate chips on low-speed until fully incorporated.
1 (12-ounce) package semi-sweet chocolate chips
Cover the cookie dough tightly with plastic wrap and refrigerate for at least 1 ½ hours.
Preheat the oven to 350°F (177°C). Line three large baking sheets with parchment paper or silicone baking mats.
Using a 1.5 tablespoon cookie scoop, scoop the cookie dough and drop onto the prepared baking sheets, making sure to leave a little room between each ball of cookie dough.
Bake for 11 to 13 minutes or until the edges of the cookies are lightly browned and the tops are set.
Remove from the oven and cool on the baking sheets for 5 to 10 minutes, then transfer the cookies to a wire rack to cool completely.
Video
Notes
Storage Instructions: Cookies may be stored in an airtight container at room temperature for up to one week.Freezing Instructions: Cookies will freeze well for 2 to 3 months. Thaw to room temperature before serving. The cookie dough will also freeze well for up to 3 months. Thaw overnight in the fridge and bake as directed.Chocolate Chips: You may replace the chocolate chips with another baking chip, like toffee bits or peanut butter chips. Feel free to swap some or all of the chocolate chips with chopped pecans or walnuts as well!Want to add cinnamon? I personally prefer these cookies without cinnamon, but you can add 1 teaspoon of ground cinnamon to the cookie dough for a subtle spiced flavor.