Preheat oven to 350°F. Prepare three 8-inch round pans with baker's floured spray (or grease and line with parchment rounds).

Pour in egg whites and mix on low until just incorporated. Mix in the buttermilk on a low speed. Add in vanilla and oil, 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, and cool completely before frosting. Set in the fridge or freezer to accelerate the cooling process if desired.

Once the layers have fully cooled, they can be leveled and any caramelized bits can be trimmed from the sides / top of the cake using a serrated knife if desired. Be sure the layers are completely cooled or chilled before trimming, so they don't crumble or break!

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.

If you've cut centers out of two of your cake layers, those will be your bottom two layers. Place a smear or two of frosting on your cake circle (to keep the cake from sliding) and center your first cake layer in the center of the circle. Spread the layer with frosting. Repeat with the second layer.

Fill the empty centers of your cake with candy, and put the final layer on top!

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)!)

Slowly drizzle alternating colors of 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. Return cake to the fridge or freezer to set the drips.

Now you’re ready to decorate the top of the cake! Pipe a ring of frosting swirls around the edge of the cake, and decorate with sprinkles. I had the most purple candy melt ganache left over, so I poured it over the top of the cake and smoothed it with an offset spatula before adding more sprinkles on top – swirling the three colors would work as well!

I can't find the ‘Witchful Thinking’ mix in the photo online anymore; it's either discontinued or sold out. But this 'Witches Brew' mix on Amazon has similar colors with spider and witch hats!

And you’re done! Cut in, watch the candy spill out – and enjoy!