Preheat oven to 375 F. Sift flour, baking powder and salt. Cream butter and sugar until smooth and yellow. Add flour mixture alternately with lemon juice. Beat egg whites until stiff peaks form. Carefully fold in egg whites and lemon peels into batter. Fill greased muffin tins 2/3 full with batter. Combine 2 tablespoons sugar and cinnamon. Sprinkle 1/2 teaspoon over each muffin. Bake for 15 to 20 minutes.