BACK
SHRIMP
1½ pound shell-on large shrimp
Kosher salt
¼ cup plus 1 Tbsp. Old Bay seasoning
3 lemons, halved
2 tablespoons olive oil
2 tablespoons chopped fresh flat-leaf parsley
MUSTARD-LIME DIPPING SAUCE
½ cup mayonnaise
2 tablespoons mustard
1 teaspoon fresh lime juice
1 teaspoon honey
1 teaspoon light brown sugar
Hot sauce
Kosher salt
Lime wedges (for serving)
SHRIMP
Step 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.
Step 2: Bring a large saucepan of salted water to a boil and add ¼ 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. Transfer to a bowl of ice water and let cool. Drain and pat dry.
Step 3: Just before serving, whisk oil and remaining 1 Tbsp. Old Bay in a medium bowl. Add shrimp and parsley and toss to coat.
Step 4: DO AHEAD: Shrimp can be cooked 1 day ahead. Cover and chill.
MUSTARD-LIME DIPPING SAUCE
Step 5: Whisk mayonnaise, brown mustard, lime juice, honey, brown sugar, mustard powder in a medium bowl; season with hot sauce and salt. Serve shrimp with dipping sauce and lime wedges.