3 lbs sweet potatoes (about 6 medium), ends trimmed, peeled, rinsed and cut into ¾”-thick rounds 2 T vegetable oil 1 tsp table salt ground black pepper
Toss potatoes in large bowl with oil, salt, and peper to taste until evenly coated. line 18x13” heavy-duty rimmed baking sheet with aluminum foil and coat with nonstick cooking spray. Arrange potatoes in single layer on baking sheet and cover tightly with aluminum foil. Adjust oven rack to middle position and place potatoes in cold oven. Turn oven to 425 and cook potatoes 30 mins.
Remove baking sheet from oven and carefully remove top layer of foil. Return potatoes to oven and cook until bottom edges of potatoes are golden brown, 15-25 mins.
Remove baking sheet from oven and, using thin metal spatula, flip slices over. Continue to roast until bottom edges of potatoes are golden brown, 18-22 mins longer. Remove from oven; let potatoes cool 5-10 mins. Transfer to platter and serve.