In your food processor, combine onion, garlic, celery, rosemary and parsley. Pulse until coarsely ground.
Melt butter in a heavy skillet over medium heat. Add in the onion mixture and sauté for 3 to 5 minutes, stirring frequently.
Add in the beer, Old Bay, red pepper, black pepper, Worcestershire sauce, lemon zest and juice. Bring to a simmer.
Add the shrimp to the hot liquid and cook over medium heat, stirring frequently. Once the shrimp turns pink and begins to curl, remove from heat.
Serve immediately, in a deep bowl, with lots of sauce and sourdough bread for dipping.
