Marinate lamb in mixture of ground spices and sour cream for 30 minutes. In a Dutch oven or flameproof casserole over medium-high heat, fry onion in mixture of oil and butter until edges are nicely browned. Add cinnamon, cloves, cardamom, garlic and ginger and continue frying for 1 or 2 minutes until onion turns medium brown. Add marinated lamb to onion mixture and stir over medium to medium-high heat until sour cream disappears and lamb is no longer pink on the outside, about 2 minutes. Stir in crushed fennel seeds, coconut milk, salt, and 3/4 cup water; bring to a boil. Turn heat down and simmer, covered, for 30 minutes. Uncover and simmer for another 20 to 25 minutes to thicken sauce, adding more water if sauce is too thick. At this point the meat and sauce should have darkened somewhat. Stir in lemon juice and remove from heat. Taste and add salt if needed.
Recipe courtesy of Maya Kaimal, author "Curried Flavors"