Preheat oven to 400°. Peel yams, then slice crosswise 1 in. thick. Sprinkle wood chips in a large roasting pan. Set a baking rack over chips. Pour in 1/4 in. water. Put yams on rack, cover with foil, and roast until a knife slides in easily, 1 hour.
Mash yams. Stir in remaining ingredients and a little hot water if they seem stiff.
*Find at well-stocked markets and online.