In a large mixing bowl, combine key lime cake mix, eggs, shortening, and lime zest.
Roll into 1-inch balls, and place on ungreased baking sheets.
Slightly flatten each dough ball.
Bake at 350 degrees for 8-10 minutes, or until edges are lightly golden.
Remove to a wire rack to cool completely.
Meanwhile, to prepare buttercream, pulse macadamia nuts and coconut oil in a food processor until smooth. You are basically creating homemade nut butter. Process it until it's as smooth as you can get it!
Transfer the macadamia nut butter to a large mixing bowl.
Add the unsalted butter, and beat to combine.
Add enough powdered sugar to create a frosting that is thick, but spreadable, between 2.5-3 cups.
Add in coconut extract.
Beat until light and fluffy, about 3-4 minutes.
Pipe or spread frosting between two cookies. Enjoy!!