These juicy key lime cupcakes are always a hit. The secret ingredient is a box of lime jello in the mix to make them green. Straight out of the oven, the warm cakes are poked with a toothpick and infused with a lime simple syrup, then filled with lime curd. This totally amps up the tartness factor! Topped with a dollop of limey cream cheese icing and you are in key lime heaven!