How do you  bake a potato in foil in oven?
 1 Heat oven to 400° F. Pierce each sweet potato several times with the tines of a fork. 
2 Place the sweet potatoes on a rimmed baking sheet lined with foil. 
3 Bake until tender, about 45 minutes. 
4 Make a slit in the top of each sweet potato. 
5 Top with 1 tablespoon of butter and season with the salt and pepper. 