Combine flour, 1/2 cup sugar, baking powder and salt in medium bowl. Beat egg lightly in small bowl. Stir in milk, 2 1/2 teaspoons lemon zest, lemon juice and oil. Add liquid to flour mixture, stir just until moistened. Fill greased muffin cups 2/3 full. Combine remaining 3 tablespoons sugar and 1/2 teaspoon lemon zest. Sprinkle over tops of muffins. Bake at 400 degrees 20 minutes. Makes 12 muffins.