Step 1

Melt butter in a medium saucepan over medium heat. Add flour; cook, whisking, about 2 minutes. Add thyme and mustard, then gradually add beer, whisking constantly until smooth. Bring to a boil and cook 1 minute more.

Step 2

Reduce heat to medium. Add cream cheese, a piece at a time, whisking constantly until smooth. Whisk in cheddar and Gruyere, a handful at a time, until melted. Remove from heat. Add Worcestershire. Season with salt and pepper. Serve, sprinkled with pretzel crumbs, with pretzel rods and celery.