Cover beans with cold water, cover and refrigerate overnight.
Drain breans and put into a 6-quart saucepan. Add 2 quarts of water and bring to a boil. Reduce heat, simmer, covered for 45 minutes. Drain.
Preheat oven to 325 F. Heat butter in a large skillet, saute the onions until golden. In a 4 quart Dutch oven, arrange in layers half the potatoes, half the onions, and half the drained beans. Sprinkle with a teaspoon of salt and 1/8 teaspoon of pepper. Repeat the layers and seasoning.
Heat bouillon and bay leaf to boiling, pour over the vegetables in the Dutch oven. Rub lamb with rosemary and place on top of the vegetables. Bake uncovered, 2 1/2 hours, or until lamb is medium well (160 F).
Arrange sliced lamb on vegetables and garnish with parsley.