In large, deep pot, sauté Spanish onion until golden. Add celery and carrots.

In the same pot, brown roast on each side five minutes. Add salt, pepper, and wine.

Cook for two and a half to three hours, depending on size (cook longer for larger roast; two hours for individual slices).

Remove roast from pot. Add sliced onion, mushrooms, and water-flour mixture. Boil until mixture thickens. Serve roast with the vegetable sauce.