Preheat oven to 350°F. Line two 7-inch pans, one 6-inch pan, and two 4-inch pans with parchment rounds, and grease with non-stick cooking spray.

Mix together all dry ingredients (flour, baking powder, sugar, and salt) in a stand mixer with a paddle attachment until fully combined.

Mix chunks of room-temperature butter slowly into the dry mix, on a low speed. Continue to mix until no large chunks of butter remain, and the mixture becomes crumbly.

Pour in egg whites, and mix on low until just incorporated. Mix in the buttermilk in two installments, on a low speed.

Add in vanilla and oil, and mix at a low speed until fully incorporated. Scrape down the sides of the bowl with a spatula, then beat on low speed for about 15 seconds (the key is to mix until the ingredients are JUST incorporated, so that the batter isn't over mixed). 

If desired, add in green gel food coloring. Mix the color in by hand using a rubber spatula, scraping the sides and bottom of the bowl part way through. Mix until the batter is evenly colored.

Divide batter between the prepared cake pans, filling each pan with the same height of batter.

Bake for 32-35 minutes, or until a toothpick comes out with a few moist crumbs. Allow the pans to cool for 10 minutes, then run an offset spatula around perimeter of the pan to separate the cake from the pan.

Place cake layers into the freezer for 45 minutes, to accelerate the cooling process. Once the layers are fully cooled, carefully flip the pans and remove the layers from the pans.

Use a serrated knife to level the tops of the layers, and then frost as desired.

While the cake layers bake and cool, make the vanilla buttercream frosting.

Beat the butter on a medium speed for 30 seconds with a paddle attachment, until smooth. Slowly add in the powdered sugar, 1 cup at a time. Alternate with small splashes of cream.

Once fully mixed, add in the vanilla and salt, and beat on low until the ingredients are fully incorporated, and the desired consistency is reached. 

If the frosting is too thick, add in additional cream (1 TBSP at a time). If the frosting is too thin, add in more powdered sugar (quarter of a cup at a time).

Wait to color the buttercream until the cake is filled and crumb coated.

Next, make the edible compost cookie dough. Cream together the unsalted butter and light brown sugar in a large bowl.

Add in the salt, baking powder, instant espresso mixture, and vanilla extract. Mix on a low speed until incorporated.

Pour in the graham cracker crumbs, mini white chocolate chips, crushed potato chips, chopped pretzels, rainbow sprinkles, and butterscotch chips. Gently pulse your stand mixer or hand mixer to slowly mix in these ingredients.

Mix in the heat treated flour on a low speed. Scrape the sides of the bowl with a rubber spatula as needed.

Add in the pasteurized egg whites, and mix on a low speed.

Stack and frost cake layers on a greaseproof cake board, using a dab of frosting to help stick the first cake layer to the board. Stack the cake layers in the following order: 7-inch, 7-inch, 6-inch, 4-inch, 4-inch.

Add a thin layer of buttercream on top of each cake layer, followed by a generous layer of edible compost cookie dough.

Add a thin coat of frosting around the cake, to fully cover the cake layers. Smooth using an acetate sheet, then chill the cake in the fridge (20 minutes) or freezer (5 minutes) until the frosting is firm to the touch.

Color 1/2 cup of frosting bright yellow, and 2/3 cup black with gel food coloring. Place each frosting into a small piping bag.

Color the remaining frosting a bright shade of green with gel food coloring.

Add a second, thicker layer of green frosting to the cake, and smooth using an acetate sheet.

Use a fork to add texture to the frosting and create the Grinch's fur.

Trace the outline of the Grinch's face with a toothpick, then use the yellow and black frosting to pipe his facial features.