Gather two glass jars or airtight containers large enough to hold two pounds of shrimp plus brine. Clean them thoroughly with hot water and set aside to air dry.

Pour 8 cups water into a large stainless steel pot. Add 2 tablespoons sea salt, 2 bay leaves, 1 tablespoon black peppercorns, and 1 teaspoon coriander seeds. Bring to a rolling boil over high heat.

Add the peeled and deveined shrimp to the boiling water. Stir gently and cook for 2 to 3 minutes, until the shrimp turn bright pink and opaque.

Using a colander or fine-mesh strainer, transfer the shrimp immediately to a bowl of ice water to stop the cooking process. Chill for 2 to 3 minutes, then drain thoroughly and pat dry with paper towels.

In a large mixing bowl, whisk together 1.5 cups apple cider vinegar, 0.5 cup white wine vinegar, and 0.5 cup olive oil for 30 seconds until slightly emulsified.

Stir in 3 tablespoons yellow mustard seeds, 2 tablespoons brown mustard seeds, 4 cloves garlic, thinly sliced, 1 medium red onion, thinly sliced, 1 tablespoon red pepper flakes, 2 teaspoons kosher salt, 1 teaspoon black pepper, and 2 bay leaves.

Divide the cooled shrimp between the prepared containers and pour the brine mixture over them, ensuring the shrimp are fully submerged. Sprinkle 3 tablespoons fresh chopped dill and 2 tablespoons fresh chopped parsley on top and stir gently.

Cover the containers tightly and refrigerate for at least 4 hours before serving, or preferably 24 hours for deeper flavor.