Heat butter and oil in a large pot. Add lamb pieces and brown on all sides. Add onions and saute until soft. Stirring, add salt, pepper and boiling water. Simmer covered, for 1 hour, adding water when necessary. While meat is simmering, wash spinach thoroughly and tear leaves into small pieces. In a separate pot, steam spinach until leaves are wilted, about 3 minutes. Remove and drain. Add spinach and dill to meat mixture. Stir and simmer for 15 minutes. Remove pot from heat. Beat eggs until frothy. Slowly add lemon juice, beating constantly. Add 1 cup of liquid from meat mixture, at first slowly and then increasing the flow, beating constantly. Pour avgolemono sauce into the lamb and spinach and stir gently to combine. Serve hot with crusty bread for soaking. Makes 6 servings. Note: If you wish, you may substitute romaine lettuce for the spinach.