Chocolate Mint Brownie Cake

Thick chocolate cake layers with mint buttercream frosted in chocolate ganache. Tastes just like the classic BYU Mint Brownie dessert!

3/4 cup buttermilk room temperature
3 whole large eggs room temperature
1 large egg white room temperature
2/3 cup sour cream room temperature
1/3 cup vegetable oil
1 Tablespoon vanilla
1 teaspoon mint extract
1 15.25oz Box Cake Mix - Dark Chocolate Fudge or Devils Food Cake I used Duncan Hines brand for the best taste and texture, but whatever brand you find will be similar.

1 cup (2 sticks) unsalted butter Left out at room temperature for 10 minutes to slightly soften
pinch of salt
1 Tablespoon pure vanilla
1/2-1 teaspoon mint extract Start with 1/2 teaspoon, then taste it. If you'd like it to be more minty, add in the other 1/2 teaspoon.
1/4 cup heavy cream
5 cups powdered sugar
1 tiny drop of leaf green gel coloring

Preheat the oven to 325 degrees (Convection bake. If you're doing convention bake, you may just need to leave them in the oven longer is all). Prep two 8" cake rounds with a swipe of shortening and a dust of flour. Set aside.
In a large bowl, whisk together all the cake ingredients except for the cake mix. Sift in the cake mix and gently fold it in (don't overmix!). Divide the batter between the two prepared cake rounds. Bake for 27-30 minutes.
Flip the cakes carefully out onto a wire rack to cool completely, wrap up in plastic wrap, and store in the freezer until the cake layers are nearly frozen.

In the bowl of a stand mixer fitted with a paddle attachment, whip up the butter until it's light and fluffy. Add in the salt, mint extract, vanilla, and heavy cream and beat again until it's uniform. Slowly add in the powdered sugar 1/2 cup at a time with the mixer speed on low. Add in a touch more heavy cream if needed.
Turn the mixer on high speed and whip up for about 2 minutes until the buttercream is lighter in texture. Add a small amount of green gel coloring and whip up again.

In a large glass bowl, stir together the chocolate melts and heavy cream. Microwave for 1 minute and stir. Heat it again for about 30 seconds and stir again. Repeat until the ganache is smooth when stirred. Let cool for about 30 minutes (stirring occasionally) until the ganache is "spreadable", then add to a stand mixer fitted with a paddle attachment. Whip up for about 1 minute until the ganache is lighter in color and texture.

Add a little buttercream to the center of a cardboard cake round placed on a cake turntable. Place down the first cake layer.
Spread on a good amount of mint buttercream filling, then add on the next cake layer. Crumb coat the cake with whatever mint buttercream is left. Place in the freezer to chill for about 2 minutes.
With a wooden spoon, beat out as many air bubbles as possible in the ganache, then, working quickly, slather on the chocolate ganache on the chilled cake. Using a cake scraper, make clean edges on the sides and top of the cake. As you work, you'll notice the color darken and the texture start to solidify.
Add on a few mint leaves as garnish, Enjoy!