Note: We tested the cake in the Test Kitchen using Betty Crocker Super Moist White Cake Mix and 9-inch cake pans.
1. Prepare the boxed cake mix according to the manufacturer's instructions, substituting soda for the amount of water given and incorporating the vegetable oil and egg whites as instructed (cake mix ingredients may vary slightly by brand). Divide the cake mix among prepared 8- or 9-inch cake pans (you will end up with one extra layer of cake not needed for this recipe). Add food coloring to enhance each of the seven layers separately with bright color: turquoise, pink, yellow, orange, purple, aqua, lime. Bake according to the manufacturer's instructions.
2. When the cake layers are cool, begin assembling the final cake. Place the first layer on the cake stand or platter and top with a layer of frosting. Sprinkle over a packet of Pop Rocks. Top with a second layer of cake, and repeat until the cake is seven layers. As the layers are built, the cake will become top-heavy and may start to slide and/or fall; to help stabilize the cake, run skewers or cake dowels (available at cake and cooking supply stores) through the layers.
3. Frost the outside of the layers and sprinkle over the remaining Pop Rocks to decorate. (Note: The Pop Rocks will become sticky shortly after the package is opened and if handled. To decorate the sides, it might be easiest to empty each package onto a sheet of paper, then curl the paper and blow the Pop Rocks onto the side of the cake.)
4. To assemble the decorations, place the wax soda bottles on skewers and cover each skewer with a soda straw. Arrange the bottle-topped skewers on top of the cake to decorate.
Each of 30 Servings
Protein: 3 grams
Carbohydrates: 166 grams
Fiber: 1 gram
Fat: 25 grams
Saturated fat: 6 grams
Sugar: 128 grams
Sodium: 747 mg
Adapted from Charles Phoenix. Copyright © 2013, Los Angeles Times
Jekka McVicar is a gardening legend in her native England, and she tells Lynne about her latest project, a herb garden for the RHS Chelsea Flower Show in London with a heartfelt purpose.