Preheat oven to 350 degrees
Add Guinness and butter to a saucepan and place over medium-low heat until the butter melts. Remove from heat. Add cocoa, sugar, cinnamon, and molasses. Whisk to combine.
Combine flour and baking soda in a large bowl, whisk to combine.
Add sour cream, eggs, and vanilla to a mixer, and mix well. Add the Guinness mixture and continue mixing.
Add the flour mixture a little at a time and mix well.
Butter 3 cake pans and line with parchment OR add cupcake liners to a cupcake pan.
Evenly distribute the batter to the cake pans OR cupcake liners.
Bake until risen. Be careful not to over bake. Around 15-25 mins.