In a medium bowl, combine the shrimp with baking soda, kosher salt, and Old Bay seasoning. Toss well to coat. Let sit for 15-20 minutes.

While the shrimp brine, fill a large bowl with ice water to stop the cooking process after poaching.

Bring a large pot of water to a rolling boil, stir in a tablespoon of lemon juice, add the shrimp, and cook for 90 seconds or until pink and opaque.

Transfer cooked shrimp to the ice bath for about 5 minutes to cool, then drain and pat dry.

In a mixing bowl, whisk together mayonnaise, Dijon mustard, lemon juice, dill, Old Bay seasoning, celery seed, and a pinch of salt and pepper. Stir in chopped celery and red onion.

Gently fold the cooled shrimp into the dressing mixture to coat evenly.

Cover with plastic wrap or transfer to an airtight container and refrigerate for at least two hours or overnight to allow flavors to meld.