Polyjuice Potion black cauldron cake (slice cut)

Polyjuice Potion Cauldron Cake

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

I'd been wanting to make a cake like this for ages! A cauldron-shaped cake, topped with dry ice to make it hiss and bubble and steam – it turned out just like I wanted, and the 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 was pretty perfect! Recipe/instructions below! 

One quick recipe note -

Below is a scaled/modified version of my favorite Vanilla Cake Layer recipe, to provide thicker layers and a taller cake. If you want to use your own recipe, I recommend scaling by 1.3x to 1.5x!

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Don't forget to pin for later!

Polyjuice potion cake pinterest pin

Polyjuice Potion Cauldron Cake

Harry Potter fans - break out the secret ingredients and brew your own Polyjuice with this Polyjuice Potion Cauldron Cake!
Prep Time30 minutes
Cook Time37 minutes
Decorating time30 minutes
Total Time1 hour 37 minutes
Course: Dessert
Cuisine: American
Keyword: Halloween Cauldron Cake, Harry Potter Cauldron Cake, Harry Potter Polyjuice Potion Cake, Polyjuice Potion Cake, Polyjuice Potion Cauldron Cake
Servings: 16 servings
Calories: 875kcal
Author: Sarah H



Polyjuice Potion Cake layers

  • 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
  • 6 eggs
  • 1 ¾ cups buttermilk room temperature
  • 2 1/2 Tablespoons vegetable oil
  • 2 teaspoons Rosemary leaves (fresh or dried) (optional; ‘Lacewing flies’)
  • 1 Tablespoon Mint leaves, chopped (fresh or dried) (optional; ‘Fluxweed’)
  • 2 teaspoons Lemongrass, chopped (fresh or dried) (optional; ‘Knotgrass’)
  • 1 Tablespoon Ginger, grated (or ground) (optional; ‘Horn of Bicorn’)
  • 2 Tablespoons grapefruit zest (optional; ‘Skin of Boomslang’)
  • few lemongrass ‘hairs’ (optional - and unless you have some other ‘bit of whoever you want to turn into!’)
  • 2-3 drops liquid green & brown food color
  • Optional: add 2 ½ teaspoons clear vanilla extract if you don’t want to add rosemary, mint, lemongrass, ginger, and grapefruit!

Black Cauldron Frosting:

  • 8 ounces cream cheese (one package, softened)
  • 16 Tablespoons butter (two sticks, softened)
  • 5 ½ -6 cups powdered sugar
  • 1 cup black cocoa powder
  • 3-4 Tablespoons milk
  • 1 Tablespoon vanilla extract
  • 1/4 teaspoon salt if using unsalted butter
  • 3-4 large drops black gel food color I used Americolor
  • 2 teaspoons dried ancho chili peppers, chopped ('leeches,' optional)


  • 8 ounces black fondant (you'll see white in the video; I used my favorite buttercream fondant since I had some on hand - but black fondant would’ve been way easier to use!)
  • Small thin plastic cup or bowl (mine in the video was blue since it was the smallest/thinnest I could find, but I recommend clear or black!)


Polyjuice Potion Cake layers

  • Preheat oven to 350°F. Prepare three 8 inch round pans with baker's floured spray (or grease and line with parchment rounds).
  • Mix together all dry ingredients (flour, sugar, baking powder, 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 on a low speed. Add in oil, and rosemary +mint +lemongrass +ginger +grapefruit zest (or just add vanilla extract if you prefer) and 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 34-37 minutes (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.
  • (This is a great time to make your frosting!)

Black Cauldron Frosting:

  • 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, salt if needed, black gel color, and chilies if desired and beat until well combined.


  • Once your cakes are cool, level them (if needed). This can be done with a cake leveler or a 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.

Carving the Cauldron shape

  • With a serrated knife, trim in slightly around 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, and place it into the hole.
  • 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, to get the frosting smooth. Cover the top of the cake, making sure the bowl on the top of the cake doesn't show too much. 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, and add it to the top edge. 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.

Now for the FUN part – the dry ice!

  • Place a few 1-2-inch chunks of dry ice into the bowl in the top of the cake. Pour 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 - this is the *coolest* look, but it doesn't last more than a few minutes at full intensity so I'd add the dry ice and water right before serving the cake.



Note: Polyjuice Potion glasses - a decoration; technically edible but would be kinda gross. I used tall drink glasses and silver duct tape to make glasses resembling the ones from the Chamber of Secrets movie. I filled the glasses halfway with milk and added a touch of extra green + brown food color, and a teaspoon of oil to keep the milk from foaming over the top of the glass. Like I said, would be gross to drink - but an option to complete the look if you’re serving this at a party!


Serving: 1slice (1/16th cake) | Calories: 875kcal | Carbohydrates: 130g | Protein: 12g | Fat: 42g

Did you make this Polyjuice Potion Cauldron Cake?

Let me know how it went – or make my day and find me on Pinterest or on Instagram and tag @IntensiveCakeUnit in your photo!

You can also add a comment or a recipe rating at the bottom of the page! 🙂

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(Pictured: Cauldron Oreo Pudding Parfaits, Halloween 'Eyes in the Fog' Cake,  Poison Apple Cake
(or click / tap the photos to be taken to the recipe pages!)

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