What you need:
4 ounces of Champagne or prosecco (chilled)
4 ounces of stout (chilled)
Pour Champagne or prosecco into a flute. Top with the stout.
For a layered look, use the back of a spoon to interrupt the flow of the stout when pouring. Since there is no ice served in this drink, make sure the sparkling wine and beer are chilled.