Mix first 5 ingredients in medium bowl. Can be made up to 3 days ahead. Cover and chill. Bring to room temperature before using.
Preheat oven to 375 degrees.
Lightly pierce potatoes all over with fork. Place sweet potatoes on cookie sheet. Bake until tender when pierced with a fork, about 1 hour, but will depend on size of sweet potato.
Cut cross in top of each potato. Using oven mitts to protect hands, squeeze the potatoes gently from the sides, forcing the crosses to open. Spoon 1 tablespoon butter into each potato. Serve, adding the remaining butter to taste.
