In a mixing bowl, mash the ripe bananas until smooth. This will give your bars a rich banana flavor.
Cream together the softened butter and granulated sugar until light and fluffy.
Beat in the egg and vanilla extract until well combined.
In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add the dry ingredients to the banana mixture, mixing until just combined.
If desired, fold in chopped nuts or chocolate chips to add extra flavor and texture to your bars.
Spread the banana sugar cookie batter evenly into a greased 9x13-inch baking pan.
Bake in a preheated oven at 350°F (175°C) for 20-25 minutes or until the edges are golden brown and a toothpick inserted into the center comes out clean.