1. Preheat oven to 350 degrees and line pans with cupcake liners.

2. In a small bowl, sift cake mix to remove any lumps.

3. In a large bowl, gently whisk egg whites, oil, buttermilk, lemon juice, sour cream and lemon zest together.

4. Combine wet ingredients with the cake mix and stir until well combined.

5. Fill cupcake liners 3/4 full and bake for 15-20 minutes or until an inserted knife comes out clean.

6. Lemon Glaze: Place all ingredients in a bowl and whisk until smooth. The mixture should reach a consistency similar to tomato soup. (I can't think of anything else to liken it unto)

7. Spoon glaze over cupcakes that are nearly cooled and let the glaze set.

8. Buttercream: Beat butter and cream cheese for 2 minutes. Scrape down bowl and add vanilla and cocoa. Slowly add powdered sugar until you reach your desired consistency.

9. Pipe buttercream over glazed cupcakes and top with yellow sprinkles or lemon slices.