Preheat your oven to 350 degrees F. Grease a 9 inch springform pan and line the bottom with parchment paper.
Whisk together flour and baking soda in a medium bowl. Set aside.
Whisk eggs in a medium bowl. Add sour cream and vanilla and whisk again until combined. Set aside.
In a large saucepan with at least a 3 quart capacity, heat cubed butter and stout over medium heat until butter is melted. Remove from heat.
Whisk in granulated sugar and cocoa powder until combined.
Pour in egg mixture and whisk to combine.
Slowly add flour and baking soda mixture while whisking until combined.
Pour batter into prepared pan.
Bake for 45 minutes, or until a toothpick inserted in the center is removed clean. Place pan on a wire rack to cool.
Once cake has cooled, remove cake from pan and place on a cake platter.