I use to make these with cookies but they are so much better with cake.
I just bake some yellow cake, I fill up the cupcake pan a little less then half way with the cake batter. Then for the meat I use chocolate cake and add about 1/4 of the way full. I cut them all in half so I have the top bun and the bottom and two meats per chocolate cupcake. I use white frosting for the mayo and tint some more white frosting red, yellow and green so ketchup, mustard and lettuce. I think I will roll out a spearmint leaf next time for the lettuce or just tint some coconut like I use to with the cookies. They were so easy and everyone loved them.
Oh and yes that is sesame seeds on the top.