Ingredients:

• 1 small white onion, finely minced (about 1/2 cup)
• 1 1/2 pounds large shrimp, shell on (see recipe note)
• 2 teaspoons kosher salt, plus more for salting the water
• 1 pound unsalted butter, at room temperature
• 2 teaspoons lemon zest
• 2 tablespoons lemon juice
• 1 tablespoon Worcestershire sauce
• 1/4 cup finely chopped fresh parsley
• 1/4 cup finely chopped fresh dill
• 1/2 teaspoon freshly ground black pepper
• 1/2 teaspoon celery seed