Polyjuice Potion Cauldron Cake

All my Harry Potter fans - I've got your next cake recipe! ;) 

I joined a ‘Happy birthday Harry’ cake collab on Instagram – partially because I’ve been wanting to try a cake like this for ages! A cauldron-shaped cake, topped with dry ice to make it hiss and steam – whole thing made my geek heart so happy!

Since I wanted to base the cake recipe on the Polyjuice Potion recipe, I found the potion supply list and loosely lined the ingredients up with the flavor profile of the ‘Witches Brew’ ice cream that Salt & Straw ice cream shops were making last Halloween season! It’s an ODD flavor profile, and you could certainly leave out any ingredients you don’t like! But the batter looked remarkably similar to the Polyjuice potion brewed by Hermione Granger in the movie, and the look of the cake when it was done made me SO happy! Recipe/instructions below!


(Disclosure: As a way to keep my kitchen stocked with butter, sugar, and flour I am a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for me to earn a commission by linking to Amazon.com and affiliated sites.
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Polyjuice Potion Cake layers:
Note - this is a modified version of my favorite Vanilla Cake Layer recipe which I modified from ChelSweets.com - I highly recommend checking out her site if you haven't before; she does amazing work! 

4 cups all-purpose flour
3 ½ cup  granulated sugar
3 teaspoon baking powder
1 ¼ teaspoon  salt
1 1/4 cup unsalted butter (or 2 ½ sticks) room temperature
(Optional: add 2 ½ teaspoons clear vanilla extract if you don’t want to add the odd ingredients below!)
6  eggs 
1 ¾ cups buttermilk, room temperature (or buttermilk powder with water is an option if you can’t find liquid buttermilk at your grocery store!)
1/8 cup (28 grams) vegetable oil
2 teaspoons / 7-8 leaves rosemary, fresh or dried (‘Lacewing flies’)
1 tablespoon / 4-5 leaves chopped mint leaves, fresh or dried (‘Fluxweed’)
2 teaspoons chopped lemongrass, fresh or dried (‘Knotgrass’)
1 tablespoon fresh ginger, grated (‘Horn of Bicorn’)
¼ cup grapefruit zest (‘Skin of Boomslang’)
handful of lemongrass ‘hairs’ – unless you have some other ‘bit of whoever you want to turn into!’
2-3 drops liquid green food color + large drop of brown gel food color



Preheat oven to 350°F. Line four 7 inch pans (for taller layers) or three 8-inch cake pans with parchment rounds, and /or grease with non-stick or baker’s floured cooking spray.

Mix together all dry ingredients (flour, baking powder, sugar, and salt) in a stand mixer with a paddle until fully combined.

Mix chunks of room-temperature butter slowly into the dry mix, on a low speed. Continue to mix until no large chunks of butter remain, and the mixture becomes crumbly.

Pour in eggs and mix on low until just incorporated.  Mix in the buttermilk in two installments, on a low speed. Add in oil, and rosemary +mint +lemongrass +ginger +grapefruit zest OR vanilla mix at a low speed until fully incorporated. Scrape down the sides of the bowl with a spatula, then beat on medium speed for about 30 seconds.

Divide batter evenly between the prepared cake pans (I find a kitchen scale helpful for this part). This guarantees your layers will bake to be the same height.

Bake for 35-37 minutes if using 8-inch pans, or 37-38 minutes for 7-inch cake pans (or until a toothpick comes out clean). Allow cake layers to cool for 10-15 minutes on a wire cooling rack before removing from pans – it helps to run an offset spatula or knife around the perimeter of the pan first. Cool completely before frosting. Set in the fridge or freezer to accelerate the cooling process if desired.

While you’re waiting – make your frosting!

Black Cauldron Frosting:
8 oz (one package) cream cheese, softened
16 Tablespoons (two sticks) butter, softened
5 ½ -6 cups powdered sugar
1 cup cocoa powder
4-6 Tablespoons milk
1 T vanilla extract
1/4 t. salt (if using unsalted butter)
1-2 teaspoons black gel food color (I used Americolor)
2 teaspoons chopped dried ancho chili peppers + 1 teaspoon ground nutmeg (‘leeches’)
Beat together softened cream cheese and butter; slowly add in powdered sugar alternating with cocoa powder and milk until frosting reaches desired consistency. Add vanilla, chilies, nutmeg, black gel color, and salt if needed and beat until well combined.

Additional Supplies/Equipment:
- 1 8- or 10 -inch cardboard cake circle (I prefer Wilton’s center-punched circles)
- Cake leveler, cake turntable, large offset spatula, and pastry cutter/bench scraper - not all 100% necessary but incredibly helpful! (Here’s a link to the cake turntable I use)
- Serrated knife for trimming your cake to a cauldron shape
- about 1 pound of fondant (I used my favorite buttercream fondant since I had some on hand, but black fondant would’ve been easier to use!)
- small piece of acetate– you could just use a small offset spatula, but acetate maker smoothing the frosting easier! Cutting down an acetate roll is the cheapest way I’ve found to buy it!
- small thin plastic storage cup or bowl – I used small plastic bowl cut down to size (mine in the video was blue since I had one on hand, but I recommend clear or black!)  

- small piece of dry ice + hot water – dry ice can be found at most large grocery stores; I called ahead to the store to make sure they had some on hand. I also recommend oven mitts (these Marauder’s Map mitts are pretty awesome!) and a pair of tongs so you don’t ice-burn yourself! Adult supervision required here.

Once your cakes are cool, level them (if needed/desired). This can be done with a cake leveler or a large serrated knife and a ruler. Place a smear of frosting on your cake circle (to keep the cake from sliding while you decorate it) and center your first cake layer in the center of the circle. Spread the layer with frosting and add the next layer on top. Repeat the process with your remaining cake layers.

Take your serrated knife and trim the bottom edge of the cake to make it rounded like the base of the cauldron. Carve a piece out of the top of the cake large enough to fit your plastic cup/bowl.

Now you're ready to crumb-coat . If you're unfamiliar with crumb-coating, it's just what it sounds like – spreading a thin layer of frosting over the entire outside of the cake to keep crumbs out of your final layer. I usually do this with my large offset spatula.
Once your crumb coat has set (this takes about 5-10 minutes in the fridge), add your final layer of frosting and smooth. I used an offset spatula to start, and then an acetate sheet to finish this part, and made sure the bowl on the top of the cake wasn’t showing. Once your cake is covered and smooth, place it into the fridge or freezer to set the frosting.

Now – add the accents with bits of fondant! Roll a piece long enough to rim the top of the cake. Shape 1 ½ - 2” pieces of fondant into cauldron ‘feet’ and space at the base of the cake. Roll 6-8” long pieces into thin rolls, and press into the sides in a small rectangular shape to resemble handles. Press out and cut a small flat rectangular piece to form the rest of the  handle, and press in over the top part of the handle.  Paint your accents black with a bit of gel color if using white fondant.

Now for the FUN part – the dry ice! I carved out a small hole from the top of the cake, and placed a small plastic cup in the hole, using more frosting to hold it in place. This was where I put a few 1-2-inch chunks of dry ice and poured about ¼ cup of hot water over the top to make them ‘melt’ (I think ‘sublime’ is the technical term?) and turn into gas/steam.

Note: Polyjuice Potion glasses! I used tall drink glasses and silver duct tape to make glasses resembling the ones from the Chamber of Secrets! I took some extra green + brown food color and added it to milk, and added a bit of dry ice to each glass! I did quickly discover that it quickly foams over the top of the glass, so I added a couple of teaspoons of oil to each one to make the bubbles pop more quickly. Option to complete the look if you’re serving this at a party!

Make this recipe? Let me know  how it went - or find me on Pinterest or on Instagram and tag @IntensiveCakeUnit in your photo!

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