Bake the chocolate and vanilla cakes and allow them to cool completely.
While the cakes and baking the cooling, prepare the icing and color it green with gel coloring.
Place a chocolate cake on a cake stand.
Use a spatula to spread icing on top of the cake.
Place the vanilla her cake on top of the icing and press gently.
Use a spatula to spread icing on top of the cake.
Place the final chocolate cake on top of the icing and press gently.
Cover the entire cake in icing. It does not need to be neat and if there are crumbs, that's perfectly fine because this is a "crumb coat" and it will all get covered.
Fill a piping bag with green icing and attach the grass tip (Wilton Tip # 233).
Start piping from the bottom of the cake and work your way upwards until sides are fully covered in "fur." The general motion is to hold your piping bag at a 45 degree angle and then squeeze the bag until icing comes out. Then, pull away gently and let the "shags" fall.
Pipe the top of the cake in the same manner. Start piping from the outer edges and work your way inwards until top is fully covered in "fur." This is very similar to how I decorated my Cookie Monster Cake and Cookie Monster Cupcakes. Push the topper gently into the center of the cake until it's secure.
Decorate with sprinkles and candies around the topper. Also, toss some sprinkles around the sides of the cake too. Enjoy.