Put remaining vanilla frosting in a medium bowl. Stir in milk-chocolate frosting and red and yellow food color, a little at a time, until frosting is the color of a hamburger bun.

To assemble: Place 1 cake layer on serving plate. Cover with bun-colored frosting. Arrange lettuce on top and around edges. Place remaining cake layer on waxed paper. Cover with chocolate-fudge frosting. Press crushed chocolate-snap cookies into frosting to simulate a hamburger patty. Using pancake turners, lift patty onto lettuce-lined bun. Spoon mustard about 1 in. from edge of top of burger, letting some run down sides. Top with tomato slices.

Trim hump (where cake has risen) off bowl cake. Place cake trimmed side down on waxed paper and frost with remaining bun-colored frosting. Lift onto tomato-topped burger. Glue eyes in position with frosting. Press pignoli nuts in place. Serves 16