Line twenty-four 2 1/2-inch muffin cups with paper bake cups; set aside. In a medium bowl combine flour, baking powder, soda, and salt. Set aside.
In a large mixing bowl beat butter with an electric mixer on medium to high speed for 30 seconds. Add sugar and beat until well combined. Add eggs, 1 at a time, beating well after each. Add flour mixture and buttermilk or sour milk alternately to beaten mixture, beating on low speed after each addition just until combined. Stir in lemon peel and lemon juice (batter may appear slightly curdled). Divide evenly among prepared muffin cups.
Bake in a 350° oven for 15 to 18 minutes or until a wooden toothpick inserted near the center of the cupcakes comes out clean. Cool cakes in pans for 5 minutes; remove from pans and cool thoroughly on wire racks.**.
When completely cooled, pipe or spread with Lemon Cream Cheese Frosting. Decorate as desired with additional piped frosting, edible flowers (pesticide-free), shaved white chocolate, and lemon zest. Store frosted cupcakes in a covered container and keep refrigerated. Makes 24 cupcakes.
Lemon Cream Cheese Frosting: Finely shred 1 teaspoon lemon peel; set aside. In a medium mixing bowl combine two 3-ounce packages cream cheese, softened; 1/2 cup butter, softened; and 1 teaspoon lemon juice; beat with electric mixer on low to medium speed until light and fluffy. Gradually add 2 cups sifted powdered sugar, beating well. Gradually beat in 2 1/2 to 2 3/4 cups additional powdered sugar to make frosting that is easy to spread. Stir in the lemon peel. If desired, tint some of the frosting with pink gel icing color for decorating.
*NOTE: To make sour milk, place 1 tablespoon lemon juice or vinegar in a glass measuring cup, then add enough milk to make 1 cup. Let stand 5 minutes before using.
**MAKE AHEAD: Freeze unfrosted cupcakes in a freezer container for up to 3 months. Bring to room temperature before frosting. The frosting can be made up to 3 days ahead, covered, and refrigerated. Set out at room temperature to soften enough to spread.