Begin by scrubbing the Yukon Gold potatoes under cold water, removing any dirt. Slice them into ¼-inch thick rounds, ensuring uniformity for even cooking.

Cut two pieces of heavy-duty aluminum foil measuring 18x12 inches each. Place one piece on a clean surface and layer a thin spread of butter down the center to help prevent sticking.

On the buttered rectangle, layer half of the potato slices in an even distribution. Sprinkle them generously with kosher salt, freshly cracked black pepper, minced garlic, and diced onion. Add small pats of butter on top of the first layer.

Repeat the layering process with the remaining potato slices. Drizzle a bit of olive oil for extra browning and flavor, then top with more seasoned butter. Carefully place the second piece of foil over the layered potatoes, sealing the edges tightly.

Preheat your grill to medium-high heat, around 350°F. Place the foil packet on the grill and cook for about 15-20 minutes on one side. Keep an eye on the grill to avoid any burning, flipping them halfway through for even cooking.

After flipping the packet, grill for an additional 10-15 minutes until the potatoes are tender and lightly crisped on the edges. Remove the packet and let it cool before unwrapping to serve.