1. In a large bowl, combine the flour, sugar, baking powder, baking soda and salt; cut in butter until mixture resembles coarse crumbs. Whisk the yogurt, egg whites, lemon juice, peel and extract; stir into crumb mixture just until moistened.
2. Fill greased or paper-lined muffin cups three-fourths full. Bake at 350° for 18-22 minutes or until a toothpick inserted near the center comes out clean. Cool for 10 minutes before removing from pan to a wire rack to cool completely. Yield: about 1 dozen.