Cut a piece of aluminum foil approximately 18 inches long (use either heavy duty foil or two pieces). In the center, toss together potatoes, onion, corn, and garlic. Top with butter slices, salt, and pepper. Close packet by pulling up the long edges, folding them together, and then folding in the short sides to seal the edges of the foil packet.
Using a grill or an oven set to 375°F, cook for approximately 30 minutes, until potatoes are tender. Toss to combine, mix in parsley, and serve!
Notes
You can also add the parsley during the cooking process - I like the freshness it adds when garnished.