Preheat the oven to 350°F (175°C). Grease and line two 8-inch cake pans.
In a large mixing bowl, whisk together the flour, cocoa powder, sugar, baking powder, baking soda, and salt.
Add the eggs, milk, oil, and vanilla extract. Beat until well combined.
Stir in the boiling water until the batter is smooth (it will be thin).
Divide the batter evenly between the two cake pans and bake for 28–30 minutes or until a toothpick inserted in the center comes out clean.
Let the cakes cool in the pans for 10 minutes, then transfer to wire racks to cool completely.
Spread a layer of chocolate frosting on top of one cake layer, then place the second layer on top and frost the top and sides of the cake.
Press the KitKat sticks vertically around the frosted sides of the cake until fully covered.
Pour M&M’s or other candies over the top of the cake.
Optional: Wrap a decorative ribbon around the cake to secure the KitKat bars and add a festive touch.
Chill for 15–30 minutes before serving to help the cake set.