Ahead of time: Soften the cream cheese and butter.

Preheat oven to 350 F. Add 18 lime green cupcake liners to muffin tins and spray with non-stick cooking spray.

Prepare the cake mix as directed on the box. Add the Lime essential oil to the batter. Pour evenly into the 18 prepared muffin tins. Bake in the preheated oven for 22 to 24 minutes, or until golden brown on top.

Remove from the muffin tins and let cool on cooling rack to room temperature. (If you don't let them cool completely, the frosting will melt and fall off the cupcakes...which is fine if you like melty frosting!)

While the cupcakes are baking, mix up the key lime frosting. Add all frosting ingredients to stand mixer or mixing bowl and beat for 3-4 minutes, or until smooth. Taste and add more lime essential oil if you wish to have a stronger lime flavor. To make the frosting to your preferred thickness, add more powdered sugar to thicken, or a drop or two of milk to thin out the frosting. Add a piece of plastic wrap over top of the frosting in the bowl and place in the refrigerator if your kitchen is too warm while the cupcakes cool down.