In the bowl of a stand mixer with the paddle attachment, add the flour, sugar, cocoa powder, baking soda, and salt. Mix on low for a minute to combine dry ingredients, then add softened butter 1 Tablespoon at a time until well incorporated into the dry ingredients and no lumps of butter are visible.

Next, whisk eggs, buttermilk, and vanilla together until well combined. With the mixer on low, add wet ingredients to dry ingredients in a steady stream until no dry ingredients are visible. Scrape down the bowl and beat for another 20 seconds.

Fill the three pans evenly - I find a kitchen scale helpful for this part, and each of mine weighed out to about 550g. Bake for 30-35 min or until a toothpick inserted 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 your cake layers are cool, level them (if needed). This can be done with a cake leveler or a large serrated knife and a ruler. Ensure cake layers are well-cooled or chilled before decorating. (This is a great time to start prepping your frosting and ganache for the filling and drip!)

Beat together softened cream cheese and butter; beat in peanut butter until thoroughly combined. Slowly add in powdered sugar alternating with milk until frosting reaches a spreadable consistency.

Meanwhile, make your ganache. Place chocolate chips in a heat-proof bowl. Add whipping cream and microwave on half power in 30-second intervals, stirring in between until smooth. Transfer to a squeeze bottle or piping bag.

(This peanut butter frosting recipe has a different texture than buttercream frostings, and I found plastic spatulas and cake scrapers worked a little better than my metal ones to spread/smooth the frosting!)

Place a bit 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 a sprinkle of Reese's Pieces candy and a drizzle of chocolate ganache if you'd like, and add your next cake layer on top.

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 10 minutes in the fridge), add your final layer of frosting and smooth. Again, I used a small plastic knife and plastic bench scraper. Once your cake is covered, place it into the fridge to set the frosting.

(Option! I mashed the cake tops with a bit of frosting to make a ‘cake pop’ mix; I wanted the Reese’s box to stand a bit taller above my cake than it would have otherwise – so I mounded some chocolate cake pop mix on top of the cake while I was decorating. Mash the cake tops with a bit of frosting to make cake pop mix now if you want to do this…. otherwise you can just eat the cake tops! 😉 )

Take the small paring knife and cut a slanted slice out of the cake – check out about 0:12 of my video if you’re unsure how to make the cut! With a small spatula or knife, crumb coat the inside of the cut you just made, and press Reeses Pieces into the frosting, filling your ‘geode’ cut in the cake.

Okaaaay...the drip! Re-warm ganache if needed to a moderate temperature – it should feel slightly warm and still be fairly liquid. A spoon will work; you'll just have a little less control. (I recommend a test drip to check temperature / consistency.)

Slowly drizzle ganache around the upper edge of your cake (except the geode), pausing every inch or so to let ganache fall in a drip down the side of the cake. Return cake to the fridge for about 10 minutes to set the drips.

Mound cake pop mix on top of the cake (optional). Open the box of Reese’s Pieces and insert your skewer (or straw) into the box. I cut a side tab off so that I could close the box, but you could also leave all four tabs open. Invert the box and press the skewer down through the cake pop mix mound into the top of the cake.

Annnd you’re done! Step back and admire your kick-butt cake!