• Pre-heat oven to 350 degrees and line 2 cupcake tins with cupcake papers.
• Place Guinness and cubed butter in a large saucepan over medium heat. Whisk until butter melts; remove from heat.
• Whisk in brown sugar and cocoa powder.
• In a separate small bowl, whisk together the sour cream, eggs, and vanilla. Whisk this mixture into the Guinness mixture.
• In a separate large bowl, sift together flour, baking soda, and salt. Fold this mixture into the Guinness mixture. Take care not to over-mix; a few lumps in your batter is OK.
• Bake cupcakes for 18-21 minutes, until a toothpick stuck into the center comes out clean. Let cupcakes cool in pan for a few minutes before moving to racks to cool completely. 
• Once cupcake are cooled, frost with Guinness Frosting. I use a Wilton #1A tip to frost mine. Top with sprinkles if desired.

Guinness Frosting

• In the bowl of a mixer or in a large bowl with a hand mixer, beat butter on medium speed until it’s nice and fluffy, 2-3 minutes.
• Add confectioners’ sugar one cup at a time and beat until well-combined. Mix in salt.
• Add Guinness and beat until combined. If frosting is too thin, add more confectioners' sugar a couple tablespoons at a time.