Preheat over to 350 degrees F. Line 13x18-inch half sheet pan with parchment paper and set aside. Melt butter and chocolate together over a bain-marie. Once completely melted, remove from heat and stir in sugar.
Whisk in eggs one at a time making sure each egg is fully incorporated before adding the next one.
Combine cocoa powder, espresso powder and salt together. Stir into chocolate mixture. Fold in flour
Pour out the batter onto a half sheet tray lined with parchment paper. Spread the batter evenly with an offset. Bake for 30-35 minutes.
Divide the marzipan in half. Color one orange. I used a combination of lemon yellow and electric orange gel paste from AmeriColor. Color the other one, green. I used a combination of lemon yellow from AmeriColor and a dark green gel color I got from Williams-Sonoma.
Roll out the orange into a thin sheet and cut out little squares.
Roll out the green into a thin sheet and using your fingers, tear pieces to the size of lettuce you want.
Cream the butter and sugar until pale and fluffy. Add the vanilla paste and continue to mix until combined. Divide the buttercream into two small bowls. Color one yellow and the other red.
You can easily find marzipan at the supermarket. I also found them at Target and Wal-mart stores.