5 ounces (3/4 cup) dark or semisweet chocolate chips
2 tablespoons coconut oil
12 ounces marzipan
Green liquid or gel food coloring
Powdered sugar, for dusting
Red liquid or gel food coloring
1 1/2 cups powdered sugar
6 tablespoons heavy cream
Yellow liquid or gel food coloring
To make the cakes: Preheat the oven to 350°F. Grease a half sheet (18x13-inch) pan and a quarter sheet (13x9-inch) pan, and line the bottoms with parchment paper.
In a large bowl, whisk together the sugar, flour, salt, baking powder and baking soda. In a medium bowl, whisk together the eggs, buttermilk, vanilla, oil and water. Add the wet ingredients to the dry ingredients and mix to combine. Transfer 3 1/2 cups of the batter to the half sheet pan and spread it out evenly. Sift the cocoa powder into the remaining batter, stir to combine, then pour it onto the quarter sheet pan and spread it out evenly. Bake the cakes until a toothpick inserted into the center comes out clean, about 15 minutes.
Let the cakes cool in their pans. Using a 2 3/4-inch round biscuit cutter, cut out 20 vanilla cake rounds and 10 chocolate cake rounds. (Note: covering the cakes and freezing them for an hour or overnight will make the edges of the circles cleaner, but this step isn't necessary.) Cake scraps can be reserved for making cake truffles, as snacks, or any other use you'd like.
Combine the chocolate chips and coconut oil in a microwaveable bowl and microwave in 30-second increments, stirring after each, until just melted and smooth. Place the chocolate cake rounds on a wire rack with a baking sheet or plate underneath to catch any excess chocolate, and pour the melted chocolate over the cakes to coat the tops and sides. Place them in the refrigerator to allow the chocolate to firm up.
To make the fixin's: For marzipan 'lettuce,' knead 4 ounces of the marzipan with a few drops of green food coloring (if the marzipan gets sticky, dust it with a little powdered sugar). Divide it into 10 equal parts, then flatten it out with a rolling pin or your palm to make flat rustic shapes that are slightly larger than the cakes.
For marzipan 'tomato slices,' knead the remaining 8 ounces marzipan with a few drops of red food coloring (if the marzipan gets sticky, dust it with a little powdered sugar). Roll it out to a 1/8- to 1/4-inch thickness, and cut out ten 2-inch rounds.
To make the 'mustard frosting,' in a bowl mix together the powdered sugar and heavy cream until smooth. Add a few drops of yellow food coloring. Transfer it to a piping bag fitted with a small plain tip or a zip-top bag with a small piece of a corner snipped off.
To assemble the cakes, stack them up in this order: a layer of vanilla cake, a squiggle of mustard, a layer of chocolate cake, lettuce, tomato, more mustard, another layer of vanilla cake, and a sprinkle of sesame seeds. Enjoy!