Preheat the oven to 350ºF (177ºC) and prepare three 6-inch cake pans or two 8-inch cake pans by spraying the sides with baking spray and fitting the bottoms with a parchment cake circle.

Place all of the dry ingredients into the bowl of a stand mixer and stir on low for 30 seconds to fully combine them. Add the vegetable oil, eggs, vanilla extract, peppermint extract, and buttermilk and mix on low until just combined. With the mixer still on low, add the hot coffee (or hot water) in a slow stream, then turn the mixer to medium and beat until smooth, about 2 minutes. The batter will be very thin.

Pour into prepared cake pans no more than ⅔ full and bake for 30-35 minutes, until a wooden toothpick inserted comes out clean. Cool completely.

With a hand mixer or paddle attachment on your stand mixer, cream the butter on medium-high until it’s creamy and light (almost white) in color. About 7 minutes.

Add the powdered sugar a few cups at a time, mixing on low and scraping down after each addition to make sure each is fully incorporated before adding the next one. Add the heavy whipping cream, vanilla extract, peppermint extract, and salt and mix on medium-low for another two minutes until fully incorporated.

Add a few drops of green food color gel until the desired shade of mint green is reached. Then, gently fold in the chopped chocolate.

Place chocolate chips into a heat resistant bowl (glass or metal).

In a saucepan over medium-high heat, warm heavy whipping cream until it just starts to boil. I always look for small bubbles forming around the edge and a soft boil starting in the middle. When you see that it’s just starting to boil, pour it into your bowl of chocolate and let sit for one minute.

Whisk it together until it’s uniform in consistency and there are no bits of chocolate left on your whisk. Cool ganache at room temperature for about 30 minutes, or until the ganache itself is room temperature.

Once the mint chocolate cake layers are cooled, level them to your desired height and place the first one on top of a cardboard cake circle, ensuring it stays put with a swipe of buttercream between the cake and cardboard. Add a layer of mint chocolate chip buttercream as filling, followed by a layer of crushed Thin Mint cookies. Place the next cake layer on top and repeat the filling and stacking process before placing the final cake layer, upside down, on top. Crumb coat the cake with mint chocolate chip buttercream and place it into the refrigerator for at least 20 minutes to let the frosting firm up.

To create the design pictured, frost a smooth finish on the cake with mint chocolate chip buttercream and place it into the refrigerator for at least 20 minutes to let the frosting firm up before adding the chocolate ganache. Once the chocolate ganache has reached room temperature and the cake finish is chilled, drip the cake with it (here is a great tutorial on how to drip cakes). Place back into the refrigerator for at least five minutes before finishing the cake with swirls of mint chocolate chip buttercream and more Thin Mint cookies.