Step 1

Preheat oven to 425°F. Line a large rimmed baking sheet with aluminum foil; set aside. Bring a large pot of water to a boil over high. Add potatoes; cook, undisturbed, 10 minutes. Add corn; cook, undisturbed, 5 minutes. Drain; transfer potatoes and corn to a large bowl.

Step 2

While potatoes and corn cook, place butter, parsley, shallot, mustard, lemon zest and juice, and 1 tablespoon of the Old Bay in a small microwavable bowl. Microwave on HIGH until butter is melted and mixture is aromatic, about 1 minute, stirring after 30 seconds. Set aside.

Step 3

Pour half of the melted butter mixture over potato mixture in bowl; toss to coat. Spread in an even layer on prepared baking sheet. Add remaining melted butter mixture to bowl (do not wipe bowl clean); add shrimp and sausage, and toss to completely coat. Spread in an even layer over potato mixture, scraping all of the butter mixture from bowl onto baking sheet. Sprinkle evenly with remaining ½ teaspoon Old Bay. Bake in preheated oven until shrimp are cooked through and sausages are hot, 14 to 18 minutes. Garnish with additional parsley, and serve alongside lemon wedges.