In a large bowl, whisk together the brown sugar and melted butter. Add the bananas and whisk well, getting rid of any clumps of banana, until the batter is smooth. It's ok if there are small pieces of banana, you just don't want large clumps.
Whisk in the egg yolk until it's combined. Then whisk in the vanilla.
Gradually whisk in the flour, baking soda, baking powder, cinnamon, and salt until combined. Switch over to a spatula and smooth out the batter, then gently fold in most of the chocolate chips, about ¾ cup.
Use a medium scoop to scoop out the batter and place onto the prepared baking sheets, about 2 inches apart (they will spread). Top each cookie with 2-4 additional chocolate chips.
Bake at 350°F for 9 to 11 minutes, just until the edges are set. Allow to cool in the pan for 5 to 10 minutes, and then transfer to a cooling rack to cool completely.
Notes
Makes 15 to 20 cookiesBaking tips:
These cookies have the consistency of banana bread, so they need to cool completely before you store them.
Store them in single layers with parchment paper or wax paper between each layer. This prevents the cookies from sticking to one another.
Store, covered, in an airtight container at room temperature for up to 4 days. You can also freeze these cookies (again, using parchment or wax paper in between layers) for up to two months.