1. Preheat the oven to 400ºF. Wash the sweet potatoes, then dry with a towel. Prick the sweet potatoes several times with a fork (this allows steam to escape as they bake).
2. Place the prepared sweet potatoes on a baking sheet lined with parchment paper or foil.
3. Bake the sweet potatoes for 45 minutes, then test for doneness (a fork or knife should be able to pierce the potato with no resistance and you should see some of the juices bubbling out the holes). If the potatoes are not soft all the way through the center, bake for an additional 10 minutes and check again.
4. After baking, let the sweet potatoes cool for 5 minutes. Slice the potatoes lengthwise, then mash lightly with a fork. Top with butter, salt, and pepper, then serve.