Preheat oven to 350 degrees. Grease and flour three 6-inch or two 9-inch cake pans.

In the bowl of your mixer, beat together butter, oil, and sugar until pale and fluffy (2-3 minutes).

Scrape down the sides of the bowl and add eggs, one at a time, beating thoroughly before each addition. Stir in vanilla extract.

In a separate bowl, whisk together the remaining dry ingredients.

Gradually alternate adding the dry mixture and the buttermilk to the butter/egg mixture (3 flour additions, 2 buttermilk additions), mixing only until just combined. Stir in green food coloring.

Evenly spoon batter into prepared pans. Bake cakes for 20-22 minutes or until a toothpick is inserted in the center and comes out clean. Cool cakes in pans for 10 minutes then invert onto a cooling rack to cool completely.

In a large HEAT-PROOF mixing bowl (preferably the metal bowl of a standing mixer), add the egg whites sugar.

Select a saucepan that the heat proof mixing bowl can set on top of, but not fall into. Fill this saucepan with several inches of water and bring to a low boil.

Place the mixing bowl with egg whites and sugar over the boiling water (similar to a double boiler set-up). Whisk the egg whites while heating until the sugar is completely dissolved - the egg whites will be warm to the touch and if you rub a bit of the egg whites between your fingers, it will be smooth. You should not feel any sugar granules. Remove from heat.

Attach mixing bowl to the standing mixer. With the WHISK attachment, beat egg white mixture on HIGH speed for 6-8 minutes. The egg whites will cool and beat into a glossy meringue with stiff peaks. Feel the bottom of the mixing bowl to ensure it is cool to the touch before proceeding on.

When the meringue has formed stiff peaks and is cooled, add the butter - 1-2 cubes at a time. Mix each addition into the meringue completely (still using the WHISK attachment) until incorporated. Continue adding 1-2 cubes of butter at a time until it is all combined.

Scrape down the sides of the bowl and switch out the whisk for the PADDLE attachment. Add vanilla extract and a pinch of salt.

Beat on the LOWEST speed using the PADDLE attachment for 4-5 minutes or until the airy mixture becomes smooth and thick like a gorgeous frosting. (see notes below for troubleshooting consistency issues).

Remove 1 cup of frosting and divide it into two bowls. Mix one bowl with grey frosting and the other bowl with purple frosting. Cover bowls with plastic wrap and set aside.

Add neon green coloring to the remaining frosting. Spoon into a large piping bag.

Level the cakes by using a serrated knife to remove the domes.

Place the first layer of the cake on a cardboard cake round or cake stand.

Clip the tip of the piping bag and pipe a ring around the perimeter of the cake. Spread ½ a cup of lime curd on the cake on the inside of the piped perimeter. Repeat with the second layer.

Top cake with final layer.

Spread a thin layer of frosting around the outside of the cake to create a crumb coat. Refrigerate or freeze the cake for 20-30 minutes.

Once cold, pipe a generous amount of neon green frosting around the outside of the cake. Run a cake scraper along the edge of the cake to flatten out the frosting and remove excess.

Using the back of a spoon or offset spatula, scrape spoonfuls of grey and purple frosting around the cake. Once again, run the cake scraper along the edge and top of the cake to flatten out the frosting and remove excess.

Gently press eyeballs around the cake.

Serve immediately or refrigerate until 30 minutes before serving.