Prick the sweet potatoes all over with a fork, then place them on a baking sheet lined with foil or a silpat mat. Bake until the potatoes are fork tender, about 1 hour or so, depending upon the size of your potatoes. Remove from the oven and let sit until cool enough to handle, about 5 minutes. Peel and discard the skins (they should come off easily with your fingers), break the potatoes in large chunks with a fork, then place the chunks into the bowl of a standing mixer fitted with the paddle attachment or a large mixing bowl.