Step 1

Combine shrimp, 1 Tbsp. Diamond Crystal or 1¾ tsp. Morton kosher salt, and 1 quart water in a medium pot. Set over medium-low heat (you want water to slowly come to a bare simmer) and cook until shrimp are just cooked through, 10–12 minutes total. Drain and transfer shrimp to a plate; let cool.

Step 2

Meanwhile, mix together sour cream, cream cheese, and remaining ½ tsp. Diamond Crystal or ¼ tsp. Morton kosher salt in a medium bowl. Mix in celery, oil, lemon zest, and lemon juice.

Step 3

Slice chilled shrimp in half lengthwise, then crosswise into ¼"-thick pieces. Fold shrimp into dressing.

Step 4

To serve, top each cracker with 1 Tbsp. dressed shrimp; sprinkle with seasoning.

Step 5

Do ahead: Shrimp can be poached and dressing made 1 day ahead. Cover and chill separately.