Mix first 6 ingredients in small bowl to blend. Stir in crystallized ginger. Season with salt and generous amount of pepper. (Can be made 3 days ahead. Cover; chill. Bring ginger-molasses butter to room temperature before using.) Preheat oven to 350°F. Pierce yams in several places with fork; bake on rimmed baking sheet until tender when pierced with fork, about 50 minutes. Cut lengthwise slit in each yam and press in ends to open top. Spoon 2 tablespoons ginger-molasses butter into each yam and serve.