Preheat oven to 350°F . Grease and flour a 9x13-inch pan or two 8-inch round cake pans.
In a large bowl, whisk together the cake mix, pudding mix, Guinness, melted butter, vanilla, salt, and sour cream.
Add the eggs one at a time, incorporating until creamy.
Beat with a hand mixer or whisk until smooth (about 2 minutes).
Pour the batter into the prepared pan and smooth the top. Bake for 35-40 minutes, or until a toothpick inserted in the center comes out clean. Remove and allow to cool completely.
When the cake is completely cooled, slather on the frosting. You can make it as thick or thin as you desire, and don't forget the sprinkles! Customize for any holiday. This cake is great all year long!