Butter two 8-inch cake pans lightly and dusts them with flour tapping out the excess, set aside.
In a large bowl, combine flour (2 cups), sugar (2/3 cup granulated sugar + 2/3 cup brown sugar), cocoa powder (1/2 cup), milk (1 1/2 cups), butter (3/4 cups), eggs (3), vanilla (2 teaspoons), baking powder (1 teaspoon), baking soda (1 teaspoon), and salt (1/2 teaspoon), with a hand-held electric mixer set on lowest speed, until ingredients are moistened. Increase the speed to medium and continue to beat batter until just combined for about 3 minutes.
Pour batter equally into the two prepared pans, using a small offset spatula to even the batter.
Place in preheated oven and bake 35 to 40 minutes or until a toothpick inserted into the center comes out clean. Set pans on a wire baking rack for 1o minutes. Slip a knife between the pan and the edge of the cake to loosen, and invert cakes onto a wire rack and cool completely.
Make Frosting:
In a medium saucepan, melt the butter (1/2 cup). Whisk in cocoa (2/3 cup) until smooth.
Alternately, add powder sugar (3 cups) and milk (1/3 cup) beating until the frosting has that spreading consistency. Thin with a little milk, as needed, if too thick.
Stir in vanilla extract (1 teaspoon).
Assembly:
Set the first layer of cake on a plater. Frost the top. Add the second layer of cake and frost the top and the sides of both layers.
Break the Kit Kats into sticks and arrange the sticks along the side of the cake.
Wrap a ribbon around the Kit Kat edge to secure the Kit Kats.
Fill the top with M & M's. Refrigerate the cake for about 4 hours to firm for ease of serving.
Notes
Chill the cake before wrapping. A slightly cool cake helps the frosting hold the Kit Kats in place and keeps the candy from sliding as you work.
Use thick frosting on the sides. The frosting isn’t just for flavor here — it’s the adhesive that keeps the candy secure, so don’t skimp.
Work one section at a time. Press the Kit Kats in gently as you go instead of trying to rush around the cake all at once.
Trim a bar if needed for a clean fit. Cutting one or two Kit Kats helps you create a seamless wrap without gaps.
Slice while cool for clean edges. A lightly chilled cake gives you sharper slices and a prettier presentation.