Once the cakes are baked and cooled, then you want to frost the bottom cake. I actually used premade frosting (which I NEVER use - but I forgot to get powdered sugar so I had no choice). To get the bun color, I mixed a little orange and a tiny bit of green. Then, I frosted the sides and top of the bottom bun. Then, I layered on the burger and frosted the brownie with chocolate frosting. I frosted it in a very lumpy way to make it look more like meat.
For the lettuce, tomato, and onions I made marshmallow fondant.
For the marshmallow fondant the recipe is 1 package marshmallows, 1 bag of powdered sugar, and 3-4 tbsp water. Microwave the marshmallows and water for about 2 minutes (until they puff up and start to melt). (ps you only need a 1/2 batch for this - but kids love this stuff, so I make a full batch and let Kamille go crazy playing with it. I keeps her busy while I make the cake.)
Word to the wise, cover your mixer with a kitchen towel before you turn it on to avoid having a spray of sugar all over your kitchen,
Knead the mixture in the stand mixer until it forms a soft, elastic dough. It should not be sticky to the touch. You may need to add more sugar or more water depending on humidity and the marshmallows you use.
When the fondant is kneaded and no longer sticky, you should have a really pliable dough, almost like gum paste. One little thing I learned is that unlike fondant, you should not roll this out on a powdered surface. Grease your cutting board (plastic or glass) or your counter top and roll it out on a greased surface. This will give you the most pliability without drying out the fondant. I used a circle cutter to make some tomatoes and onions. Then, I painted the tomatoes red (it is easier than dying the fondant) and I also made lettuce. I rolled it out very thin and then stretched the ends to make a wavy leaf. Someone - I'm not going to name names, has my fondant tools so I had to get creative in making these leaves.
