Cut Yukon Gold and sweet potatoes into 1/8-in. slices; toss with oil and sprinkle with salt and pepper. Divide between 2 greased 15x10x1-in. baking pans. Roast at 425° for 17-20 minutes or until tender., Meanwhile, in a small skillet, heat butter over medium heat. Add garlic and thyme; cook and stir for 1 minute. Transfer roasted potatoes to a large bowl. Drizzle with butter mixture; toss to coat. Sprinkle with cheeses and, if desired, additional thyme; toss to combine.