Surprise the hamburger lover in your life with a cake that looks like a large hamburger, or bring this as a dessert to a cookout. The hamburger is made entirely of edible cake, frosting and fondant despite its savory appearance. Basic hamburger toppings such as lettuce, tomatoes, ketchup and mayonnaise help pull off the charade, while chocolate and yellow cakes stand in as the meat and bun. You can even add cheesy decorations, though it would technically make the confection a cheeseburger.
Bake one round yellow cake and one shorter, round chocolate cake. Both cakes should be the same diameter. Cut the yellow cake in half horizontally with a serrated knife. Trim the chocolate cake so it's roughly the same thickness as one of the yellow cake halves. This is one instance in which a dome is desirable for the yellow cake because it helps achieve the look of a top hamburger bun.
Frost the yellow cakes with golden brown frosting for the buns. Frost the chocolate cake with chocolate frosting. You can leave the cakes without frosting if you don't like a lot of frosting and the cakes bake to the desired color.
Set the chocolate cake directly on top of the bottom bun cake. Set the top bun piece aside as you work on the toppings.
Roll out green fondant to no more than 1/4 inch thick with a fondant roller. Shape the edges with your fingers to make them wavy so they look like lettuce. The lettuce doesn't need to cover the entire chocolate cake, so make several pieces that measure about 3 inches wide and 4 to 5 inches long. Place the lettuce around the edge of the chocolate cake, allowing it to drape over the edge so you can see it from the side. Place several pieces around all sides of the cake.
Roll out yellow fondant to about 1/4 inch thick if you want to add cheese to the burger. Cut out four triangles with a single-wheel rotary fondant cutter. Place the triangles evenly around all sides of the cake with one flat side on top of the chocolate cake and the triangle points hanging down over the edge.
Roll out red fondant to about 1/4 inch thick. Cut out four or five circles from the red fondant to use as tomatoes. Place the tomatoes evenly around the edge of the chocolate cake with just a bit of the tomato sticking out further than the chocolate cake.
Add red buttercream frosting and white buttercream frosting to two separate decorating bags. Cut about 1/2 inch from the end of each bag to create an opening. Squeeze the white and red frosting all over the top of the chocolate cake and toppings, just as you would squeeze ketchup and mayonnaise on a hamburger. The sauces can drizzle down the sides of the burger, if you wish. As an alternative to red frosting, try strawberry or raspberry jam thinned out with a bit of hot water.
Set the top bun cake piece centered on top of the chocolate cake. Do not press down because you want to keep the toppings visible from the sides.
Roll out a small piece of white or tan fondant to about 1/8 inch thick. Cut out tiny football-shaped pieces of fondant to use as sesame seeds. Place the sesame seed pieces all over the top bun. If you didn't frost the top and bottom burger buns, squeeze a tiny dot of buttercream frosting on the back of the sesame seeds so they stick to the top bun.
Roll a piece of olive-green fondant into an oval shape to make an olive to fit the scale of the cake. Press a small, red fondant dot onto each end of the olive piece. If it doesn't stick easily, brush a bit of water on the back of the red dot to make it tacky. Insert a 1/4-inch diameter wooden dowel through the olive and push it down through the center of the cake to resemble a toothpick. The dowel should protrude about 6 inches above the top burger bun.