Season the sweet potatoes

Preheat the oven to 400°F(200°C). Place the potatoes in a 2-qt (2-l) gratin or baking dish. Drizzle with the oil, season with salt and pepper, and toss to coat. Spread the potatoes in a single layer.

Bake the sweet potatoes

Cover the dish with aluminum foil and bake for about 20 minutes. Uncover, sprinkle with the cheese, pine nuts, and thyme, and continue to bake, uncovered, until the cheese is golden and the sweet potatoes are tender, 8–10 minutes longer. Remove from the oven, drizzle with the lemon juice, and serve.