Slice thinly the meat from two roast ducks and steep for one hour in a mixture of tarragon vinegar, olive oil, onion juice, and pepper. Now line a dish with puff paste and bake just enough to color it. Carefully drain the slices of duck and place them in alternate layers with sausage meat in the dish. Cover with the paste, brush over with the white of an egg, and bake for an hour and a half.