Begin by washing and cutting the Yukon Gold potatoes into bite-sized cubes. In a large mixing bowl, combine the cubed potatoes with olive oil, kosher salt, black pepper, onion powder, garlic powder, fresh rosemary, and thyme. Toss everything together until evenly coated.

Grab four pieces of heavy-duty aluminum foil, cutting each to approximately 16 inches long. Lay each piece flat on your countertop, ready to hold the potato mixture.

Portion the seasoned potato mixture evenly among the four sheets of foil, placing it in the center of each. Carefully fold the edges of the foil over the potatoes, creating a sealed packet.

Preheat your grill to medium-high heat, around 400°F. Place the foil packets seam-side up directly on the grill grates. Cook for about 30 minutes, turning occasionally.

Carefully remove the foil packets from the grill using tongs. Cut open each packet and sprinkle with shredded cheddar and Monterey Jack cheeses if desired, then return to the grill until cheese melts. Serve hot with sour cream.