Preheat your oven to 375°F (190°C).
Wash and scrub the sweet potatoes, then pat them dry with a paper towel.
Pierce each sweet potato several times with a fork.
Place the sweet potatoes on a baking sheet lined with aluminum foil.
Bake the sweet potatoes in the preheated oven for 1 to 1 1/2 hours, or until they are very soft and tender.
Remove the sweet potatoes from the oven and let them cool slightly.
Peel the skins off the sweet potatoes and place the flesh in a large bowl.
Add the melted butter, brown sugar, cinnamon, nutmeg, and salt to the bowl with the sweet potatoes.
Mash the sweet potatoes with a potato masher or fork until they are smooth and well combined.
Serve the melting sweet potatoes hot as a delicious side dish.