Put lamb in a wide baking dish. Add 1/2 cup hot water and the butter, cover and put in the oven for about 2 hours at 300F. After the first half hour add the onions, salt, paprika, black pepper and the water, stir and continue cooking. Add 1/2 cup of water in another 30 minutes, stir. Repeat adding the water every 30 minutes until the two hours elapse. Cover with a baking sheet and cook for additional 1/2 hour (2.5 hrs total cooking time). Serve warm sprinkled with parsley.