Line 2 (1/2 cup-12 capacity) muffin tins with cupcake liners.
Lightly spoon 2 cups flour into dry measuring cups, and level with a knife. Combine 2 cups flour, baking powder, baking soda, and salt, stirring with a whisk.
Place granulated sugar and 1/2 cup butter in a large bowl; beat with a mixer at medium speed until well blended (about 5 minutes). Add eggs, one at a time, beating well after each addition. Add flour mixture and nonfat buttermilk alternately to sugar mixture, beginning and ending with the flour mixture. Beat in 2 tablespoons lemon rind and 2 tablespoons lemon juice.
Carefully spoon the batter into the cupcake liners, filling them about 3/4 full.
Bake at 350° for 15 minutes or until a wooden pick inserted in center of the cupcake comes out clean. Cool in pans 10 minutes on a wire rack; remove from pans. Cool completely before icing.
To make the icing, place the butter in a large mixing bowl. On the medium speed of an electric mixer, cream the butter until smooth. Add 1 cup of the sugar and a little of the lemon juice. Beat until smooth. Add 2 cups of the sugar, the remaining lemon juice and the lemon rind. Continue to beat until smooth and creamy, about 3 to 5 minutes. Gradually add the remaining sugar (if needed), beating well after each addition (about 2 minutes), until the icing is thick enough to be of good spreading consistency. You may not need to add all of the sugar.
If desired, add a few drops of food coloring and mix thoroughly. (Use and store the icing at room temperature because icing will set if chilled.