• Preheat oven to 320℉.
• Using a spatula, work the granulated sugar into the butter until you have a nice cream.
• To the cream, add vanilla extract.
• Using a whisk, incorporate three medium eggs, one at a time, mixing well in between each egg.
• Add flour and baking powder.
• Add buttermilk.
• Mix to combine. (Don't overmix.)

Dyeing the Batter

• Reserve one third of the batter to dye green for the top portion of the cake.
• Use a few drops of the paste food coloring to dye the batter green.
• Pour the batter into a seven inch prepared brownie pan. (I sprayed mine with baking spray and lined it with parchment paper.)
• Repeat the dyeing process with the yellow food coloring for the remaining two-thirds of the batter.
• Using an offset spatula, make sure that the batter is smooth in the pans. (You can give the pans a few swift taps on the countertop to get rid of any bubbles.)

Baking

• Bake in a 320℉ oven (160℃) for ten minutes, initially. (The green cake, because it is thinner, will cook much faster. So start checking it at ten minutes.) When a toothpick comes out clean, it should be done.
• The yellow cake should take an additional five or ten minutes.
• Allow the cakes to completely cool before assembly.

Assembly

• Remove the parchment paper.
• On the yellow cake, spread a layer of honey (about a tablespoon or so), just enough to act like glue.
• With a bread knife, remove a thin layer of the yellow cake around the edges, so it’s nice and fuzzy.
• Using a serrated bread knife, shave off the very top layer of the green cake to make it look fuzzy like the scrubber part of the sponge.

Cutting Cake and Finishing

• Cut cake into equal sponge-sized rectangles.
• To add soap bubbles to your sponge cake, in a mixing bowl, whisk nonfat milk until it forms bubbles.
• With a spoon, scoop bubbles onto top of cake to look like soap.