Makes One Nine-Inch Cake
For the Cake:

1 cup all-purpose flour

1 cup granulated sugar

1/2 cup good cocoa powder

1 teaspoon baking soda

1/2 teaspoon kosher salt

1 large egg, at room temperature

1/2 cup sour cream, at room temperature

1/2 cup (1 stick) butter, melted and cooled

3/4 cups Guinness Extra Stout, at room temperature