Preheat the oven to 375ºF and line two baking sheets with parchment paper.

In a small bowl, combine the flour, cornstarch, baking powder, baking soda, and salt.

In a large bowl, beat the butter and brown sugar until light and fluffy.

Mix in the mashed banana, vanilla extract, and egg until everything is well blended.

Using a silicone spatula, stir the flour mixture into the banana mixture until combined.

Gently fold in the crushed banana chips and walnuts.

Using a 1.5-tablespoon cookie scoop, drop cookie dough onto the prepared baking sheets, spacing them about 2 inches apart.

Bake for 10 minutes or until the cookies are lightly browned.

Let them cool on the pan for 5 minutes before transferring to a wire rack to cool completely.