Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper.
In a medium bowl, mash the banana until smooth. Add softened butter and sugar. Mix until creamy.
Stir in vanilla extract.
Add the flour and baking soda. Mix until combined. The dough will be soft and a little sticky—just like cookie dough should be.
Scoop heaping tablespoons of dough onto the baking sheet, spacing them about 2 inches apart.
Bake for 10–12 minutes or until the edges are lightly golden and the tops look set.
Cool on the baking sheet for a few minutes, then transfer to a wire rack. Or eat one warm—we won’t judge.