Preheat oven to 350 degrees F, and prep cake pan by greasing liberally with butter or oil, then sprinkling with cocoa powder. Shake cocoa throughout pan then dump any excess. Set aside.
In a medium saucepan, heat stout (or root beer), coffee, and butter over medium heat, stirring occasionally until butter or oil melts. Remove from heat and whisk in cocoa powder until smooth. Set aside to cool to room temperature.
In a medium bowl, whisk flour, sugar, baking soda, and salt and set aside.
In a separate large bowl or stand mixer, beat eggs and sour cream (or DF cream cheese) on medium until homogeneous, about 2 minutes.
With the mixer on low, drizzle in cooled chocolate-beer mixture, beating until just combined. Scrape down the sides of the bowl.
Add flour mixture in 3 small increments, beating on low until barely combined, then adding the next batch. Fold batter with a spatula to finish mixing, then pour into prepared pan. Do not over mix batter or your cake will be too stiff.
Bake for 30-40 minutes until a toothpick poked in the center comes out with only a few moist crumbs. Err on the side of under baking, you don't want a completely clean toothpick (aka an over baked cake).
Let cool completely on a wire rack.