Place potatoes and onion in a large bowl.
In a medium microwave-safe bowl, gently melt the butter in the microwave. Stir in olive oil, ranch dressing, and basil pesto. Depending on the flavor of your particular ranch dressing and pesto, you may want to add a bit more of each. Season with kosher salt & freshly cracked black pepper to taste. Then pour pesto ranch sauce over potatoes and onions, and fold to combine.
Tear off 6 pieces of 18" x 18" heavy-duty foil wrap. Fold each square in half to make a rectangle shape. Divide the potato and onion mixture between the 6 pieces of foil. Then bring the 2 long sides up over the potatoes so that the long sides meet. Fold them over and crease tightly. To finish the packet, fold each of the shorter ends over a couple of times and crease tightly.
Heat grill to medium.
Add packets to grill grates, creased side down and grill for 15 minutes. Flip packets over and grill for an additional 10 to 15 minutes, or until potatoes are perfectly soft when pierced with a fork. Remove from grill and open up packets to create a sort of individual "bowl". Sprinkle with fresh chives, plus additional salt & pepper if desired. Serve hot.
