Place a smear of frosting on your large cake circle (to keep the cake from sliding while you decorate it) and center your first large cake layer in the center of the circle.
(I wanted a bit more of a liqueur kick to the cake layers, so I used a jigger to infuse each one with a few tablespoons of a bourbon, espresso, and chocolate liqueur mixture. Optional but recommended!)
Pipe a small border of frosting around the outer edge of the layer, and spread a layer of chocolate filling in the middle. Add your next cake layer on top. Repeat the process with your remaining cake layers.
Next, repeat the same process with your smaller cardboard circle and cake layers. Of note – if your circles aren’t pre-center-punched, be sure to grab a dowel or straw and make your own hole in the exact center of the circle! This will allow you to center the tier on the base tier later on.
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 tiers to keep crumbs out of your final layers!
Once your crumb coat has set (this takes about 5-10 minutes in the fridge), add your final layers of frosting and smooth. I like to use an offset spatula and bench scraper for this part. (For my larger tier, I was able to smooth the frosting fairly well free-handed, but I struggled getting the sides smooth on my smaller one. Setting a second small cake circle on top and using it as a guide for smoothing my icing worked much more easily!)
Once your base tier is covered, place the icing comb on the cake circle against your cake and run the comb around the cake to texture the frosting (if desired). Place both tiers into the freezer for about 20 minutes to set the frosting and get the cake cold enough to set the drip.