3/4 cup quick-cooking oats
1 3/4 cups all-purpose flour
1/2 teaspoon salt
1 teaspoon baking powder
12 tablespoons unsalted butter, softened
2/3 cup granulated sugar
1/3 cup firmly packed brown sugar
1 large egg
1/2 teaspoon vanilla extract
1 large banana. mashed
1 1/4 cups walnuts, toasted and chopped
Preheat oven to 350°F (175°C).
Combine oats, flour, salt, baking powder in a medium bowl; set aside.
Using an electric mixer, cream the butter and sugars together until smooth. Add in the egg and vanilla extract and continue beating until incorporated. Mix in mashed banana.
Stir in oat/flour mixture and walnuts into the sugar mixture. Spoon the dough about 1 1/2-inches apart on parchment lined cookie sheets.
Bake until light brown, about 15 minutes, turning cookie sheets halfway between baking to ensure even browning.