Defrost the shrimp by placing them in the refrigerator overnight or running cool water over them for 15-20 minutes.

Prepare an ice bath in a large mixing bowl by combining ice and cold water.

Poach shrimp in a pot of heated water with kosher salt until they turn bright orange and opaque, about 2.5 to 3.5 minutes.

Transfer the cooked shrimp immediately to the ice bath to stop the cooking process and preserve texture.

Make the dressing by whisking together mayonnaise, sour cream, dill, mustard, lemon juice, lemon zest, minced garlic, and salt until smooth.

Mix cooled shrimp, chopped celery, and diced red onion with the dressing until well-coated.

Serve immediately or refrigerate for up to 5 days; enjoy over lettuce, in a sandwich, or with crackers.