In Part 1 of How to Make a Popcorn Box Cake, we covered baking the cakes that will be used to create the popcorn box cake. In today’s post, we will cover the process of building the popcorn box out of cake.
I would estimate that the building stage took about 3 hours of effort with some chill time and a hockey game in between.
Cut the Cakes
- Trim the cakes: The recipe asks you to trim the tops so the cakes are extremely flat, and to trim the caramelized crust off the sides. Her measurements are extremely precise. If you don’t like precise measurements and using a ruler, the popcorn box cake is not the right project for you. Just go do something else that will make you happier. S’Mores are nice. Everybody loves a good S’more and they require absolutely no measuring.
- Cut each cake into 4 even sized squares. They are going to be used to make two separate vertical piles of four cakes. Organize your fridge so that you have room to refrigerate two separate 4 layer stacks which will be iced separately before being combined into a single eight layer tower. You will eventually need a fridge shelf with enough height for the whole eight layer cake.
Make the Icing
- Make the caramel Italian meringue buttercream icing. The icing requires 8 egg whites and more butter than you can possibly imagine in one place at one time. I didn’t want to waste 8 egg yolks so I bought a carton of pasteurized egg whites. Note that the icing is a meringue, which requires a candy thermometer to precisely heat the sugar/water mixture before adding it to the egg whites. Luckily, I own one . . . but it turns out my candy thermometer is in Celsius and the recipe is in Fahrenheit. The pot was already bubbling. This was not the time to notice that I had a Celsius conversion problem. Grrrr.
In case you’re wondering, it turns out that:
230 ° F = 110 °C
240° F = 116 °C
By the way, in her instructional video, Yolanda says to mix the caramel into 2 cups of the icing. Trust me, the popcorn box cake is going to need the entire icing recipe. 2 cups isn’t going to get the job done.
- Make two separate piles of four cakes, with buttercream icing between the layers. Don’t ice the top of either cake yet. Sprinkle some simple syrup on top to keep the tops moist. Put the two piles in the fridge for the icing to harden.
This is where everything started to go wrong. Real life intervened. It was 3:05 pm and Mark phoned on his way home to remind me that I was supposed to go pick Lily up and bring her home so she could get ready quickly to leave for a late afternoon hockey game across town.
Oops. I was standing there with a candy thermometer in a pot of bubbling hot sugar with a mixer going, full of fluffy egg whites.
“She can walk,” I said. “It’s only a 20 minute walk.”
“But we have to leave soon,” he reminded me. I looked at the heap of stuff around me.
“She can hitch-hike,” I said, and hung up on him.
Mark went to pick her up.
I desperately started slopping icing on to the first stack of four cakes in a big hurry. Hurrying is always a mistake, because that is when I realized I’d forgotten to add the butter to the icing. When the phone call came I was at the stage where I was supposed to have started adding butter, but I got so flustered by the big hurry that I forgot and just started sloshing icing on cakes.
I scraped all the icing back into the bowl from the second pile of cakes, but the first pile was already stuck together like glue. I couldn’t get the pile unstuck to scrape the icing back into the mixer bowl to add the butter.
Fine, I said. There will be 4 butterless layers. There is so much butter in this thing that nobody will notice, will they? [Note: They didn’t.] But then I looked at the recipe and adding the butter to the rest required a lengthy beating time. By this time Mark was hovering, reminding me that we had to leave. I slapped some together without beating for long enough, iced the second set of 4 cakes, tossed them in the fridge, put plastic wrap on the remainder of the icing, shoved it in the fridge too and off we ran to the rink.
When we got back, about 4 hours later, the icing in the bowl was in a sad state. Separated, weeping, grainy. Just a sorry mess.
I went to the Serious Eats website. They diagnosed the problem and had an antidote. The icing was too cold. I followed their instructions. Heating the remaining icing over a pot of steaming water and then rebeating it in the mixer fixed the problem entirely. It was time lost, though.
Build the Box Shape
- Build the “Popcorn Box”.
This requires sticking the larger cardboard insert to the top of one of the four-layer cake piles with icing. Then put icing on top of the cardboard and use it to glue the second pile of cakes on top to make the full eight layers.
You will need to measure and cut support dowels to the exact height of the top four-layer stack. I bought food-safe dowels from the baking store, and used an Exacto knife to cut them and trim the ends so there were no splinters.
The dowels will then be inserted into the top cake for structural support. The picture at the top shows the dowels going in so that you can see how they are placed.
Ice the top and use that to stick the smaller cardboard support square to the top. I covered the cardboard inserts with tin foil because they are touching food and I didn’t know how clean those things are as they are sold unwrapped.
The cake will be flipped over at a later stage. The cakes that are on the top at this point will be the bottom in the final popcorn box cake. Cut a diagonal A-line shape, using the edges of the two cardboard inserts as your cutting guide, so that the top is narrower than the bottom at this point. (When it is flipped to its final position, the bottom of the cake will be narrower and flare to towards the top, which will be the broader opening of the popcorn box.)
Take the eventual total weight of the cake (I would estimate about 10 pounds) into account when selecting the working base that you are going to use to carry it back and forth between the fridge and the table. I forgot that it was going to be flipped and made the mistake of putting the larger, sturdier support base under the end that wound up being the top. There was no way that I was going to try to shift the 8 layers from one support base to another so I just made do. I also forgot to measure for the overhang of the fridge light when I moved the fridge shelf down to hold the eight layer cake.
Carve the Popcorn Box Cake
More problems. Yolanda Gampp of How to Cake It provides very precise measurements for the cakes and the cardboard inserts. And yes, I measured precisely. Both the cake and the insert were the specified size, but I felt that the cardboard insert in the middle was be too big to permit a nice diagonal A-line for the popcorn box cake. I had to pull the upper pile of cakes off, fish the cardboard insert out and trim the square back by ¼” and re-ice everything. There was icing all over everything. That size worked fine.
The next step is to cut the diagonal shape for the popcorn box, using the cardboard inserts as a guide. Sounds easy, but it isn’t. The top four layers kept sloshing around because I had removed and re-iced the top stack to make the cardboard smaller, and the icing hadn’t set yet. You have to cut by eye and I’m not as precise as Yolanda. I tried, but, well, Yolanda is perfect and I am but human. I did my best.
Lily: “It’s crooked.”
Me: “But the upper 4 layers were sloshing around. The layers kept moving with the motion of the knife.”
Lily (unimpressed): “It’s lopsided.”
I iced it as smoothly as I could and popped it in the fridge. I was cheap and didn’t buy the big bench scraper. It really would have helped smooth the icing surface, but honestly it didn’t matter in the end as the buttercream is totally covered by the fondant.
In Part 3, we will cover the fondant decorating.
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