Preheat oven to 350 degrees F (180 degrees C).
Over a large bowl, sift together the All-Purpose Flour (1 1/3 cup), Baking Soda (1 teaspoon) and Unsweetened Cocoa Powder (1/3 cup). Make a well in the center, and crack in your Egg (2).
Melt Butter (1/2 cup) and add to the bowl along with Vanilla Extract (1 teaspoon), Buttermilk (1 cup) and Caster Sugar (1 cup). Beat with an electric mixer for about 4 minutes, or until thick and creamy.
Pour into a lined and greased springform pan, and spread evenly. Bake for 40-45 minutes. Remove from pan, and allow to cool for 2 hours.
Cut off the outer border of the cake, so it is roughly the thickness of a Kit Kat.
In a large bowl, sift together the pure Powdered Confectioners Sugar (1 1/3 cup) and Unsweetened Cocoa Powder (1 1/2 tablespoon). Add boiling Water (to taste) and mix until a thick, smooth paste is formed.
Place cake onto the bottom round of a springform pan. Spread the icing mixture around the edges of the cake. Replace the outer ring onto the pan.
Open the packs of Kit Kat® Crisp Wafers in Milk Chocolate (40 piece) and break them up into pieces of two. Place them around the outer edge of the cake, and then refrigerate to let the icing set.
In the bowl of a stand mixer fitted with the whisk attachment, add the small carton of Whipping Cream (1/2 pint). Whisk on high until soft peaks form. Beat about 20 seconds longer to form stiffer peaks.
Spoon cream onto cake, and spread evenly. Sprinkle with M&M's® Milk Chocolate Candy (2 package) and return to the fridge for 30 minutes. Remove from pan, serve, and enjoy!