In medium bowl, toss cheese with flour.
Heat beer in, 4-cup glass measure at HIGH 1 1/2 to 2 minutes, or until boiling.
Gradually add half of cheese, Worcestershire and mustard, stirring until smooth.
Cook at MEDIUM 1 1/2 to 2 1/2 minutes; stir once.
Add remaining cheese.
Cook at MEDIUM 2 to 3 minutes, or until cheese is completely melted; stir once.
Serve, traditionally, over toast points.