Place potatoes in a medium saucepan; add enough water to cover. Bring to a boil; reduce heat to medium-low and simmer for 15 to 20 minutes or until fork-tender. Drain; cool. Meanwhile, peel shrimp, leaving tails attached; cover and refrigerate.

Stir together Cheddar cheese, cream cheese, mayonnaise, ⅓ cup pimientos, mustard, Worcestershire sauce and cayenne pepper in a medium bowl; set aside. Cover and refrigerate until ready to use.

Melt 1 Tbsp. butter in 12-in. cast iron skillet over medium heat. Add onion and celery; cook for 2 minutes, stirring frequently. Stir in sausage; cook for 3 to 5 minutes or until sausage is browned, stirring frequently. Transfer from skillet to a medium bowl.

Pat shrimp dry with paper towels. Melt 1 Tbsp. butter in same skillet over medium heat. Add shrimp; sprinkle with Creole seasoning. Cook for 3 to 4 minutes or until shrimp reach 145°, stirring frequently. Stir in remaining pimientos. Transfer from skillet to another medium bowl.

Place oven rack 4 to 5 in. from heat. Preheat broiler to HIGH.

Cut each cooked potato into 4 wedges. Melt remaining 1 Tbsp. butter in same skillet over medium-high heat. Add potato wedges; cook for 2 to 3 minutes or until potatoes are lightly browned. Add corn and garlic; cook for 3 to 4 minutes more or until corn is tender, stirring frequently. Return sausage mixture to skillet; stir gently to combine. Remove from heat.

Dollop 9 to 10 spoonfuls of pimiento cheese mixture on top of skillet mixture. Broil for 1 to 2 minutes or until cheese mixture begins to melt. Arrange shrimp mixture on top. Broil for 1 minute more or until heated through. Garnish with parsley sprigs, if desired.