Preheat oven to 350 F. Line cupcake pan with liners.
In a small box, mix together the margarita mixer, tequila, and Grand Marnier.
In a large bowl, mix the cake mix, egg whites, canola oil,and lime zest. Add in the margarita mixture the from previous step. Mix on low for 30 seconds, then increase speed to medium for two minutes. The batter may be slightly lumpy.
Spoon the batter into the cupcake pan. ( I highly recommend using a Bakelicious Cupcake Batter Spoon – it measures out the perfect amount of batter every time You can find it online or at Hobby Lobby). Bake for 20-25 minutes depending on oven or until toothpick inserted into cupcake comes out clean. Let cupcakes cool before frosting.
Prepare frosting:
In a large mixing bowl, add butter, and beat with electric mixer until fluffy.
Add the salt, lime juice, and the lime zest. Add powdered sugar one cup at a time. Mix until consistency is thick. Add more powdered sugar if needed.