FOR THE SAUCE: Whisk all ingredients together in bowl. Cover and set aside while potatoes cook.
FOR THE POTATOES: Adjust oven rack to middle position and heat oven to 400 degrees. Toss potatoes, oil, granulated garlic, onion powder, salt and pepper together in bowl.
Arrange potatoes in single layer on rimmed baking sheet. Roast until potatoes are tender and deep golden brown on bottoms, 35 to 40 minutes. Sprinkle potatoes with cheddar, return sheet to oven and continue to roast until cheese is melted, about 3 minutes longer.
Transfer potatoes to platter. Sprinkle with cilantro and dill. Serve with sauce.
Original recipe called for 1/4 C olive oil and 8 oz. sharp cheddar cheese. If you are using garlic powder instead of granulated garlic, cut the amount called for in half.