Lamb Braised in Yogurt and Cream

1 cup plain yogurt
1 cup heavy cream
2 medium onions, coarsely chopped
1/4 cup blanched almonds
2 tablespoons chopped fresh ginger
2 tablespoons ground coriander
1 tablespoon ground cardamom
Salt and freshly ground pepper to taste
2 lb. boneless lean lamb, cut into 2.inch pieces
1 to 2 lb. potatoes, peeled and quartered

Combine all ingredients except the lamb and potatoes in an electric blender or food processor
and process until smooth. Put the yogurt mixture and the lamb into a large, heavy pot
(preferably non-stick) and bring to a boil over moderate heat. Reduce the heat and simmer
tightly covered for 2 hours.
Check the stew and stir frequently, adding milk or water as needed if the sauce
becomes too thick. Add the potatoes and continue cooking until tender, 30 to 45
minutes.