1. Increase oven temperature to 365°F.
2. At 3,500 feet, add an extra 1 tablespoon of flour. For each additional 1,500 feet, add one more tablespoon.
3. Decrease the granulated sugar by 1 tablespoon and the brown sugar by 1/2 tablespoon.
4. In a small bowl, beat an additional egg. Add 1 tablespoon of the egg mixture at 3,000 feet. For each additional 1,000 feet, add another 1 1/2 teaspoons.
5. At 3,000-5,000 feet, adjust baking powder to 1 1/2 teaspoons and baking soda to a little less than 1/2 teaspoon. For higher altitudes, reduce the measurements further.
6. Baking time may decrease to 16-18 minutes.
For more info on high-altitude baking, visit King Arthur Flour's website.