I made this pizza cake for my husband to surprise him on Valentine's Day (he is a pizza lover). I made a box cake (yellow) in a 16 inch pizza pan (parchment lined and sprayed with Pam). I froze it and the next day flipped it over out of the pan.
I used a small amount of cocoa powder mixed with water to make a "paint" to tint the edges of the cake crust. I made the sauce with a can of frosting tinted with red (and some orange) food coloring and cocoa powder (to make it darker). I even added cut up red gummi bears to look like chopped tomatoes in the "sauce". I added some green candy sprinkles chopped up to look like oregano in the sauce ( I had to pick the green ones out of the multi-colored sprinkes). I rolled some white/clear and green gumdrops flat and cut into strips for green peppers and onions. You will need to roll the strips into powdered sugar a bit when making as these are really sticky.
I also melted a couple green gummi bears in the microwave on a piece of parchment paper and let cool and cut into strips for more green pepper and onion as I ran short on gumdrops. I rolled flat a few mini marshmallows and shaped into mushroom slices and then brushed cocoa powder on them to look more realistic.
For black olives I bought a box of Crows (like Dots candy, but all black) and sliced them into slices and cut holes in the middle. I tried using a cherry pitter to make the holes but they were way too hard and sticky.
For pepperoni slices I made fondant (for the 1st time ever) and colored with red, orange food color and cocoa powder. I even sprinkled in some flecks of white fondany crumbs to look like fat in the pepperoni. I sprayed with cooking spray so that they were easier to get off the parchment (and the shine looked more realistic).
The cheese was a grated white chocolate bar and also I added some white icing as I could not get the "cheese" to melt with a kitchen torch or a hairdryer which just blew the "cheese" off the pizza.