Halloween Slime Cake

I LOVE getting to use Halloween colors on cakes!

I saw a Halloween cake years ago that STILL sticks in my memory. It was black with a simple green drip, and I LOVED the way it looked! Not long afterward I also found an Erlenmeyer flask (think tapered-top beaker) on sale at a craft store. That was all it took for me to decide to turn a cake design I already loved into a "science-experiment-gone-wrong" Halloween Slime cake! 😉

It was the EASIEST Halloween cake I think I’ve ever done, and I LOVED the look and the taste! Wanting to make whole recipe super-easy to make, I doctored up a couple of boxed cake mixes for the cake layers. It worked beautifully! A scratch recipe is also linked in the FAQs for all my cake purists. 😉

Let me tell you – this cake disappeared SO fast when I took it into work! Recipe, tips, and links to everything I used are below!

(Disclosure: As an Amazon associate I may earn from qualifying purchases, and my posts often contain affiliate links. If you click a link and make a purchase, I may receive a commission at no extra cost to you!) 


You used boxed mixes in this recipe - can I use a scratch cake recipe instead? 

  • Absolutely! You use my Favorite Vanilla Cake recipe, or even your own favorite white or vanilla cake recipe - just add 3-4 large drops of bright/lime green gel food color to the batter before baking. 

Do I have to make the frosting from scratch? 

  • Not if you don't want to! You can substitute chocolate store-bought frosting and add black gel color, though the shade of black may be a little lighter.
    Store-bought frosting is usually a little thinner than my recipe; add 2 Tablespoons of regular or black cocoa powder at a time until you reach a consistency that spreads and stays in place on the cake well. 

Halloween Slime Cake

One of my MOST popular Halloween cake - a bright green drip and a Erlenmeyer flask make the perfect Halloween Slime Cake!
Prep Time20 mins
Cook Time30 mins
Total Time50 mins
Course: Dessert
Cuisine: American
Keyword: Halloween cake, Halloween Slime cake
Servings: 16 servings
Calories: 752kcal
Author: Sarah H



Cake layers

Black cocoa cream cheese buttercream

  • 8 ounces cream cheese (one package, softened)
  • 1 cup butter 16 Tablespoons or two sticks, softened
  • 5 ½ -6 cups powdered sugar
  • 1 cup black cocoa powder Available on Amazon; this post explains why I love it so much!
  • 4-6 Tablespoons milk
  • 1 Tablespoon vanilla extract
  • 1/4 teaspoon salt if using unsalted butter
  • 3-4 large drops black gel food color use 5-6 large drops if using regular cocoa powder. I use black gel color pretty frequently, especially around Halloween, so I bought this large bottle from Americolor!

Green Cake Drip

  • 6 ounces White Candy Melts (I used Wilton Bright White)
  • 3 Tablespoons heavy whipping cream (I used an incredibly thick Costco brand; you may need a bit less depending on the thickness of your cream)
  • 2-3 drops bright/lime green gel food coloring (Add last; after candy melts are melted with whipping cream!)


Cake layers

  • Preheat oven to 350°F. Line three 8-inch cake pans with parchment rounds, or grease with non-stick or baker’s floured cooking spray.
  • Mix together all wet ingredients (butter, egg whites, buttermilk, vanilla, and gel food color) in a large bowl with a mixer or wire whisk. Blend in cake mixes for 30 seconds until moistened, then beat for 2 minutes until well combined.
  • 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 (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.


  • 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, black gel color, and salt if needed and beat until well combined.
  • 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.
  • Add your next cake layer on top, and repeat the process with your remaining cake layers.
  • 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.
  • Once your crumb coat has set (this takes about 5-10 minutes in the fridge), add your final layer of frosting and smooth. I like to use an offset spatula and bench scraper for this part. Once your cake is covered, place it into the fridge or freezer to set the frosting.
  • This is a great time to make and color your ganache drip(s)!

Cake Drip & Decorations

  • Place heavy cream and candy melts in a microwave-safe bowl (don't add the color yet!) and microwave on 50% power in 30-second intervals until smooth, stirring in between. Once the mixture is completely melted and smooth, add in the gel color and mix until the color is even.
  • Once your ganache has cooled to a moderate temperature - it should be liquid but not hot so it doesn't melt your frosting - transfer it to a squeeze bottle or piping bag. You can use a spoon; it just won't give you quite as much control. 
  • Slowly drizzle candy melt ganache around the upper edge of your cake, pausing every inch or so to let more fall in a drip down the side of the cake. Pour a bit of ganache into the Erlenmeyer flask and set it on top of the cake. Smooth any gaps or bumpy spots with a small offset spatula. Place the cake into the refrigerator to set the drips!
    And you’re done! Cut in and enjoy!



Please note nutrition information is an estimate and may not be exactly accurate. 


Serving: 1slice | Calories: 752kcal | Carbohydrates: 98g | Protein: 9g | Fat: 38g


Black Cocoa Cream Cheese Buttercream


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

2 thoughts on “Halloween Slime Cake

  1. What kind of black coloring do you use or recommend that will not make my coworkers teeth mouth or tongue black.

    1. Hi Debbie! Unfortunately, I have yet to find a black food color that doesn’t leave *some* trace of color behind. My favorite is Americolor’s black gel color – it’s never turned my teeth black, just turns your tongue a bit purple 😉. I just updated this recipe to reflect my new favorite trick though – starting with a dark chocolate frosting made with black cocoa powder allows you to get to a pretty deep black without staining everyone’s mouths much at all! 😉🖤🖤🖤

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