Ingredients

• 1 1/2 pounds shell-on large shrimp
• Kosher salt
• 1/4 cup plus 1 tablespoon Old Bay seasoning
• 3 lemons, halved
• 2 tablespoons olive oil
• 2 tablespoons chopped fresh flat-leaf parsley
• 1/2 cup mayonnaise
• 2 tablespoons spicy brown mustard
• 1 teaspoon fresh lime juice
• 1 teaspoon honey
• 1 teaspoon light brown sugar
• 1/2 teaspoon English mustard powder
• 1/2 teaspoon Worcestershire sauce
• Hot sauce
• Kosher salt
• Lime wedges (for serving)

Instructions

1. Using kitchen shears and working one at a time, cut along the length of the backs of shrimp, cutting through shells and just deep enough into flesh to expose veins; remove veins.
2. Bring a large saucepan of salted water to a boil and add 1/4 cup Old Bay seasoning. Squeeze lemon juice into water and add lemon halves to saucepan; return water to a boil. Add shrimp, reduce heat, and simmer until cooked through, about 3 minutes.
3. Transfer to a bowl of ice water and let cool. Drain and pat dry.
4. Just before serving, whisk oil and remaining 1 tablespoon Old Bay in a medium bowl. Add shrimp and parsley and toss to coat.
5. Do ahead: Shrimp can be cooked 1 day ahead. Cover and chill.
6. Mustard-lime dipping sauce: Whisk mayonnaise, brown mustard, lime juice, honey, brown sugar, mustard powder, and Worcestershire sauce in a medium bowl; season with hot sauce and salt. Serve shrimp with dipping sauce and lime wedges.
7. Whisk mayonnaise, brown mustard, lime juice, honey, brown sugar, mustard powder, and Worcestershire sauce in a medium bowl; season with hot sauce and salt. Serve shrimp with dipping sauce and lime wedges.