Step 1

Preheat the oven to 350f and set the rack to the middle level. Line a 9x13 inch cake pan with parchment paper.

Step 2

In a large bowl add the flour, cocoa powder, sugar, baking soda, baking powder, espresso powder (if using) and salt, and whisk until combined.

Step 3

In a separate large bowl add the Guinness, sour cream, buttermilk, eggs, vegetable oil, and vanilla extract and whisk until combined.

Step 4

Add the wet ingredients to the dry ingredients and use a hand mixer to beat on low for 1 minute. Alternatively, you can use a stand mixer fitted with a paddle attachment.

Step 5

Pour the batter into the prepared cake pan and bake for 50 - 55 minutes or until a toothpick inserted in the middle comes out clean.

Step 6

Allow the cake to cool for 10 minutes, then turn it over and place on a wire rack. Remove the parchment paper and allow the cake to fully cool before frosting with the Irish Cream frosting.

Step 7

In a large bowl or the bowl of a stand mixer fitted with a paddle attachment, beat the room temperature butter on medium speed for about 2 minutes or until creamy.

Step 8

Add 6 cups of confectioner's sugar, the salt, and the Irish cream and beat on low for 30 seconds then increase the speed to medium to medium-high and beat for an additional 2 minutes.

Step 9

Check the consistency of the frosting and if it's too thin, add the remaining cup of sugar a little at a time until the desired consistency is reached. If you find the frosting is too thick, you can add about a tablespoon of Irish cream at a time to thin it out.

Step 10

Scoop the frosting onto the top of the cooled cake and use an offset spatula to distribute evenly. Slice, serve, and enjoy!