Bring the beer to a boil over medium-high heat in a FINEX Cast Iron 1 quart saucepan.
Reduce the heat to medium-low so the beer is gently simmering.
Toss the Gruyère with the cornstarch in a medium bowl.
Add the cheese mixture to the beer one large handful at a time, stirring the cheese in a figure-eight pattern until completely melted before adding more.
Stir in the mustard, Worcestershire sauce, and paprika.
Season with salt, garnish with scallions and serve immediately.