TO PREPARE THE FILLET, MAKE slits in it and put slivers of garlic in the slits. Rub well with salt, pepper and Tabasco. Combine the soy sauce, olive oil, port and herbs and place the fillet in this marinade in a baking dish for at least 1/2 hour unrefrigerated, or an hour or more in the refrigerator. Turn several times while it is marinating. Preheat oven to 425F. Place the fillet on a rack in a roasting pan. Roast for 30-to-35 minutes, basting occasionally with the marinade. A meat thermometer should register 120F for very rare, 125F for rare, 130F for medium-rare. After it is removed from the oven, the internal temperature will rise as much as another 10F. Allow the fillet to rest, covered with foil, up to 30 minutes. If it needs to sit longer, you might try a catering trick: Wrap the fillet, just out of the oven, in plastic wrap. Unwrap just before slicing. Cut into slices and place on a warm platter; garnish with sprigs of watercress.