Preheat the oven to 350°F. Line baking sheets with parchment paper and set aside.
Whisk flour and cornstarch together and set aside
Mix together butter and sugars at medium speed until creamy.
Add egg yolk and maple flavoring, beating until well mixed.
Reduce speed to low and gradually add flour and cornstarch mixture and toasted pecans.
Measure dough by the scant tablespoonful and shape into balls. Place dough balls on baking sheets and press down lightly with fingers or flat bottom of drinking glass until dough is about ½-inch thick.
Bake for 9-12 minutes or until cookies puff and are very light golden brown.