Preheat oven to 350F. Place two (green) cupcake liners in each well of a muffin tin.
In a large bowl, whisk together flour, sugar, baking powder, baking soda and salt.
In another large bowl or or the bowl of a stand mixer, cream or whisk together butter, egg whites, sour cream, milk, and vanilla until combined. The batter will be lumpy.
Add the wet mixture to the flour mixture and add green food gel. Mix until well combined. Divide batter evenly between muffin wells (using a cookie scoop), filling each paper liner about ⅔ full.
Bake for 22 minutes, or until a toothpick comes out clean or the batter reaches an internal temperature of 205-210F. Cool in the muffin tin for 5-10 minutes, then remove to a cooling rack and cool completely before frosting.
To make the frosting, in a stand mixture using the paddle attachment, whip together butter and salt for 1 minute.
Add powdered sugar, about 1 cup at a time, beating on low after each addition. Scrape the bowl with a spatula, and repeat until all sugar is added.
Add 1 tablespoon of cream while mixing on low. Beat until the frosting is fluffy, adding ½ tablespoon at a time until the frosting reaches the desired consistency. Add pink food gel and mix, adding more coloring to reach the desired color.
Add frosting into a piping bag fitted with a 2D tip or your favorite tip, or add to a zip top bag and cut the corner. Start in the middle of the cupcake, and pipe frosting in a circle motion to the outside, then work towards the center to form a peak. Using small tongs, a fork, or decorating tweezers, randomly place chocolate chips.
Notes
Freeze cooled cupcakes in an airtight container for up to 4 months. Thaw completely before frosting.
Keep leftover watermelon cupcakes refrigerated in an airtight container for up to 4 days.