Celebrate St. Patrick’s Day (or any day) with this delicious Guinness Chocolate Cake! It has the most wonderful fudgy flavor and tender texture that is complemented by a Bailey's buttercream filling and a rich ganache frosting.
Preheat oven to 350 degrees Fahrenheit and spray 2 8-inch round cake pans with pan spray and a parchment round, if desired.
In a small saucepan, heat the Guinness, sugar, and cocoa powder together over medium heat until all the sugar is dissolved, about 3 minutes. Remove from the heat and let it cool for 5-10 minutes.
In a separate bowl, whisk together the oil, eggs, sour cream, and vanilla. Once smooth whisk in the oil until fully combined.
Whisk the egg mixture into the sugar mixture until combined. Gently whisk in the flour, baking soda, and salt.
Divide the batter evenly into the two prepared cake pans and bake for 40-45 minutes, until the center of the cakes spring back when lightly pressed on or a toothpick comes out clean.
Let the cakes cool completely before wrapping them with plastic wrap and chilling them in the refrigerator for at least 2 hours before assembling the cake. Cold cake is significantly easier to frost than warm or room-temperature cake.
Ganache
While the cake bakes, prepare the ganache by simmering the Guinness over low heat until reduced by half to ¼ cup. Add the cream to the pan and simmer until steaming.
Add the chocolate to a large bowl and pour the steaming liquid over it. Let the chocolate sit for 2 minutes before whisking until smooth and shiny. Cover the bowl and place it in the refrigerator to chill until the cakes are cooled and ready to be frosted.
Bailey’s Buttercream Filling
Use a hand mixer to beat the butter, powdered sugar, and Bailey’s together in a medium bowl until combined. Start with 3 tablespoons of Bailey’s and add a little more at a time until the buttercream is soft and fluffy, but not runny.
Assembly
Once the cakes are chilled and ready to be frosted, place one layer bottom side down on a cake plate or serving plate. Top with the buttercream and spread it evenly over the cake, leaving ¼-½ inch space around the perimeter of the cake so the buttercream doesn't interfere with the ganache. Place the second layer of cake topside down on the buttercream.
Whip the chilled ganache with a hand mixer until soft and fluffy. Use it immediately to frost the cake, as it will set up and harden the longer it sits. If it becomes stiff as you are frosting, use the hand mixer to beat it again until it is soft.
Add a couple of large dollops of ganache to the top of the cake and use an offset spatula to spread it around, letting it go over the edges. Use the spatula to push the overhanging ganache down onto the sides, adding more from the bowl as needed. Try not to lift the spatula straight up off the cake, as that can cause the ganache to pull off from the cake bringing crumbs with it. Instead, move the spatula in a swiping motion to stop contact with the ganache.
Once the cake has been covered in an even layer of ganache, you may use the offset spatula or a bench scraper with a straight edge to smooth it. I like to run my metal tools under very hot water and dry them thoroughly before using the hot metal to smooth the ganache.