Poke the sweet potatoes with a fork all over, about six times. Place them on a baking sheet lined with foil and bake until very tender, about 45 minutes to 1 hour.
Cut the sweet potatoes in half lengthwise and, with a knife, make crosshatch marks, cutting into the potatoes about halfway through. Place the sweet potatoes on the baking sheet and set aside.
In a medium bowl, combine the brown sugar, butter, and pecans (if using). Spoon the mixture onto the 8 sweet-potato halves. Heat in oven until the potatoes are hot and the sugar and nuts are browned, about 20 to 25 minutes. Serve hot or warm.
These are excellent and easy to make. The pecan mixture is so good. I used coconut palm sugar which is all natural and low glycemic. The sweet potatoes were quite large, so once they were completely done I cut each half in half. Since it was Thanksgiving I put half a normal size marshmallow on top of each 1/4 and broiled for just a couple of minutes to brown. PERFECT!