Preparation: Mix beef, rice & five-spice powder; form into firm 1" balls. Peel yam; cut into chunks. Cut beancurd into 1" cubes. Wash mushrooms; remove dried part of stem. Cooking: Heat wok until smoking; add peanut oil. When oil is hot, braise meatballs. Add warm water, soy sauce, sherry & ginger. Bring to boil, transfer to clay pot, cover, and simmer for 30 minutes. Add yam chunks, beancurd & mushrooms. Cook uncovered another 20 minutes until yams are done but still firm. Thicken sauce with cornstarch paste; boil briefly. Turn off heat, cover to keep hot until ready to serve.