Step 1

Place the cake mix in a medium bowl.

Step 2

Add the sour cream, vegetable oil, eggs, and Guinness. Mix well.

Step 3

Spray the slow cooker with a baking spray (or just coat with a little vegetable oil if you don't have baking spray). Add the batter to the slow cooker and cook on low for 2 to 2 1/2 hours (until the middle does not jiggle when you shake the slow cooker).

Step 4

Place the heavy cream in a medium bowl. Beat with a hand mixer until the cream begins to thicken.

Step 5

Add the sugar and Guinness, and continue to beat until the cream is stiffened.