Preheat oven to 350°F. Prepare three 8 inch round pans with baker's floured spray (or grease and line with parchment rounds).

Pour in egg whites, and mix on low until just incorporated. Mix in the buttermilk on a low speed. Add in mint extract and oil, and mix at a low speed until fully incorporated. Scrape down the sides of the bowl with a spatula, then beat on medium speed for about 30 seconds.

Divide batter evenly between the prepared cake pans (I find a kitchen scale helpful for this part). This guarantees your layers will bake to be the same height.

Bake for 34-37 minutes (or until a skewer comes out clean). Allow cake layers to cool for 10-15 minutes on a wire cooling rack before removing from pans. Cool completely before frosting. Set in the fridge or freezer to accelerate the cooling process if desired.

Once the layers have fully cooled, they can be leveled and any caramelized bits can be trimmed from the sides / top of the cake using a serrated knife if desired. Be sure the layers are completely cooled or chilled before trimming. If you try to trim the layers while they’re still warm, they will crumble apart.

Beat together softened cream cheese and butter; slowly add in powdered sugar alternating with milk until frosting reaches desired consistency. Add vanilla and salt and beat until well combined.

Reserve 1 cup of frosting and mix in cocoa powder until combined, adding 1-2 more tablespoons of milk to maintain a spreadable consistency - this will be your cake filling!

Place a smear of frosting on your cake circle (to keep the cake from sliding while you decorate it) and center your first cake layer in the center of the circle. Spread the layer with frosting, and spread or pipe chocolate filling over the top of the first layer. Sprinkle a layer of chopped Milano cookies over the filling, and add your next cake layer on top. Repeat the process with your remaining cake layers.

Now you're ready to crumb-coat . If you're unfamiliar with crumb-coating, it's just what it sounds like - a thin layer of frosting over the entire outside of the cake to keep crumbs out of your final layer.

Once your crumb coat has set (this takes about 10 minutes in the fridge), add your final layer of frosting and smooth. I like to use an offset spatula and bench scraper for this part.

This part's optional, but I piped small lines of chocolate frosting onto the outside of the cake and smoothed the frosting with my cake scraper for a bit of a textured/marbled look to the outside of the cake.

Sprinkle chopped Milano cookies around the base of the cake, and press them into the cake base with your hands or the back of a spoon.

Top with frosting swirls and halved cookies, and arrange a few whole cookies on top of a frosting swirl in the center of the cake. Sprinkle the cake with cookie crumbs....and you're done! Step back, admire your work....and enjoy!