1. Preheat oven to 350º.
2. Lightly spoon the flour into a dry measuring cup; level with a knife. In a small bowl, whisk together the flour, baking soda, and salt.
3. In a food processor, process the sugars for about 1 minute until they're well mixed. With the motor running, add the butter in pieces. Process until smooth and creamy, scraping the sides of the bowl as necessary. Add the egg white and vanilla and process about 5 seconds, just until incorporated. Scrape the sides of the bowl with a rubber spatula. Pulse in the flour mixture until incorporated, about 20 pulses.
4. Unless directions say otherwise, drop dough by even tablespoons 2 inches apart onto 2 baking sheets lightly coated with cooking spray. Bake 1 sheet at a time for 15 minutes or just until the cookies begin to brown on top and are just set around the edges. Do not overbake.
5. Remove baking sheets from oven and allow cookies to sit on sheets for 2 minutes or until firm enough to lift with a small, flexible pancake turner. Transfer the cookies to racks to cool completely before storing them in an airtight container.