Peel, slice, and coarsely chop the vegetables and cook them slowly in the butter for 5 minutes. Add 6 cups of boiling water, salt and pepper, and bread, which you have first dried out in a slow oven and crumbled. Simmer the soup for a half hour and puree it. Reheat over low heat. Stir in the egg yolks beaten well with the cream. Serve at once, garnished with finely minced parsley.