Easy Guinness Chocolate Cake

For cake:
2 Heat oven to 350 degrees F.
3 Spray a 9-inch round or 8-inch square cake pan with nonstick cooking spray. (Note: If you have a pan that tends to stick, line the bottom with parchment.)
4 In a large mixing bowl whisk together flour, sugar, cocoa powder, baking soda, and salt.
5 Add oil, Guinness, and vanilla extract all at once and stir just until everything is combined and no dry spots remain.
6 Pour batter into prepared cake pan.
7 Bake until the cake is set in the middle, 27 to 30 minutes. (Note: In a thicker pan made of glass or ceramic, the cake may take up to an extra 5 minutes to cook all the way through.)
8 Allow cake to cool completely.
For frosting:
11 Combine cream cheese and powdered sugar in the bowl of a standing mixer. Turn the mixer on medium and beat until evenly combined.
12 Turn the mixer down to medium-low speed and slowly pour the heavy cream and then Bailey’s (if using) down the side of the bowl with the mixer running.
13 When all of the cream has been added, increase speed to medium-high until stiff peaks form (this could take 3 to 4 minutes; you are making whipped cream, so the frosting won't set up until it has been beat for sufficiently long). 
14 At this point, frosting can be refrigerated up to 1 day. 
15 Spread frosting on cake just before serving (after the cake has cooled completely).