Preheat the oven to 400 F. or the grill to medium-high (about 400 F). If using frozen shrimp place the package under cold water for 10 minutes to thaw.
Bring 2 quarts of water to a boil and add the potatoes and corn. Reduce the heat & bring to a simmer. Cook for 10 minutes on simmer then drain into a colander. Set aside.
While the potatoes & corn are cooking, prepare 4 sets of 12-inch by 24-inch long aluminum foil sheets. Fold each in half, forming a square. If using industrial aluminum foil simply prepare sheets measuring 12-inches square. Slightly fold up the edges of the sheets.
In a large bowl, combine the drained potatoes & corn, sausage, thawed shrimp, onion, and garlic. Drizzle with the 4 tablespoons of melted butter, season with salt, pepper (if using), & Old Bay seasoning. Mix very well to coat all of the ingredients.
Divide the shrimp boil ingredients between the four aluminum foil sheets. Neatly fold into packets, ensuring a good seal.
Place them onto a baking sheet & bake for 15 minutes. If grilling, place the packets directly onto the grill surface & cook for 15 minutes, flipping once after about 8 minutes.
Serve the packets slightly opened up, garnished with chopped parsley, a pinch of Old Bay seasoning, and a few lemon wedges. Serve the melted butter on the side for optional drizzling over the shrimp boil or for dipping.
Recipe Notes
For our meal, I did not add any salt or pepper. We found the Old Bay seasoning was enough for our liking. Just personal preference!