Baking Sweet Potatoes. 1  Preheat oven to 400°F. 2  With a fork, pierce sweet potato skin 5-6 times. 3  Place on baking sheet lined with foil. 4  Bake until tender, 45 minutes to 1 hour. With a fork, pierce sweet potato skin 5-6 times. 2  Place on baking sheet lined with foil. 3  Bake until tender, 45 minutes to 1 hour.