Preheat the oven to 400°F. Place sweet potato and onion in your baking dish. You want enough to cover the dish in a single layer of potatoes. For several servings, I use about 2-3 medium potatoes.
Cover with parchment or tin foil and bake for 30 minutes, or until fork tender. Remove the cover and place back in the oven for about 20 minutes, or until caramelized. Serve hot, garnished with chopped cilantro if desired.