I adapted this from a soda cake recipe I read online...I liked the idea of not having to add eggs and oil, but still have a great tasting, moist cake for an event I was attending...Everyone loved the cupcakes and wanted the recipe. My mother in law said it was one of the best lime flavored things she had ever eaten and I could bring her some anytime I made it again...
Combine cake mix with the Sprite and 2 tablespoons of Lime juice. Fill cupcake liners about 2/3 full of mixture and bake at 350% for approx. 18 minutes, depending on your oven, it can take a few minutes more or less, toothpick comes clean.
Mix 1 cup of the powered sugar with 2 tablespoons of lime juice, you want a slightly thick syrup consistency, a bit more of the lime juice can be added to achieve this.
As the cupcakes get done, brush the tops of each, while warm with the lime juice-powdered sugar syrup, I brush each at least twice.
Beat the cream cheese to a smooth texture, add the remaining lime-powdered sugar syrup, add the 1 cup of powdered sugar and any remaining lime juice until well blended, fold in the marshmallow fluff, frost the cooled cupcakes. This can also be made into a 13x9 sheet cake or two 8x8 square pans. I recommend chilling anything larger than cupcakes to make slicing easier. This cake is very moist, but can be crumbly. Tastes great.