1In 2-quart saucepan, melt butter over medium heat. Cook onion and celery in butter about 2 minutes, stirring occasionally, until tender.
2Stir in flour, pepper and mustard. Stir in beer and milk. Heat to boiling over medium heat, stirring constantly. Boil and stir 1 minute; reduce heat to low.
3Gradually stir in cheese. Heat over low heat, stirring constantly, just until cheese is melted. Sprinkle each serving with popcorn.