1. Prick yams with a fork several times, and place on a cooking sheet. Bake at 375° for 1 hour or until soft to the touch.
2. Meanwhile, fill a medium saucepan with water and 2 tablespoons lemon juice. Bring to a boil. Add pears, reduce heat, and simmer 6 minutes or until tender. Drain well.
3. Cool yams slightly; cut in half lengthwise, and scoop flesh into a food processor, discarding skins. Process yams, pears, tangerine juice, and remaining ingredients until smooth. Transfer to a greased 2-quart baking dish, and bake at 350° for 20 minutes or until heated through.