1. Preheat the oven to 350 degrees F and line two 9-inch cake pans with butter and parchment paper. Set to the side

GUINNESS

1. Before mixing together the cake batter, prepare the reduced Guinness.
   350 grams Guinness beer, reduced to 180 grams
2. In a small saucepan, bring the Guinness to boil over medium-high heat. Once it is boiling, reduce the heat to medium-low and allow it to simmer until it is reduced to 220 grams (¾ cup + 4 teaspoons), about 30 minutes.

   You will add 180g (3/4 c) to the batter and set aside 40g (4 teaspoons) of the reduced Guinness for the frosting. 
3. While the Guinness is simmering, start to prepare the cake batter.

DRY INGREDIENTS

1. In a medium mixing bowl, sift together the flour, natural cocoa powder, baking soda, espresso powder and salt. Add the sugars, then whisk until combined. Set to the side. 

   Note: Cocoa powder is notorious for having clumps, so be sure to not skip the sifting! This recipe calls for unsweetened natural cocoa powder, not Dutch-processed cocoa powder. The acidity of the natural cocoa powder reacts with the baking soda to help this cake rise. 
   220 grams all-purpose flour, 75 grams unsweetened, natural cocoa powder (not Dutch-processed), 12 grams baking soda, 2 grams espresso powder, optional, 6 grams salt, 200 grams sugar, 220 grams light brown sugar

WET INGREDIENTS

1. In a separate bowl, whisk together the room-temperature sour cream, eggs, neutral oil, vanilla extract and sourdough discard until smooth. 

   You can use active sourdough starter, as well. Just be sure to use the same amount in grams.
   180 grams sour cream, room temperature, 2 eggs, 115 grams neutral oil, like avocado oil, 8 grams vanilla extract, 120 grams sourdough discard

COMBINE

1. Pour the wet ingredients into the dry ingredients, then mix with a rubber spatula until there are no more streaks of flour. The batter will look very thick, like brownie batter. 
2. Pour in the hot, reduced Guinness and whisk until combined. This will thin out the cake batter.

   You want the Guinness to be hot. This helps “bloom” the cocoa powder which will enhance the cocoa flavor. 
3. Divide the cake batter evenly into the prepared cake pans. Gently drop the cake pans on the countertop to remove any air bubbles from the batter.

BAKE

1. Bake the Sourdough Guinness Chocolate Cake for 20-25 minutes. The cake is done when a toothpick comes out mostly clean with a few moist bites of cake. 
2. Remove the cake from the oven and place on a wire rack to cool completely. 

   Note: It is normal for a chocolate cake to slightly sink in the middle even when it’s been completely baked through. Cocoa powder isn’t as strong as all-purpose flour. There is a lot of moisture in this moist chocolate cake.

CHOCOLATE CREAM CHEESE  FROSTING

1. Prefer a Bailey's Buttercream Frosting instead? See my recipe in the notes!
2. In a stand mixer with a whisk attachment, beat the room-temperature butter and softened cream cheese on medium speed for 2 minutes, or until light and fluffy.

   This can also be done with a hand mixer.
   226 grams cream cheese, softened, 113 grams unsalted butter, softened
3. Next, add the powdered sugar, one cup at a time at medium speed.
   520 grams powdered sugar
4. Finally, add the cocoa powder, reduced Guinness and a pinch of salt. Mix until combined. 
   50 grams unsweetened cocoa powder, 40 grams reduced Guinness, pinch of salt
5. Directions on how to assemble and decorate below.