Place large pork shoulder roast in cooking bag, add water. Rub with garlic salt, season all, and salt. Tie bag and cut slits it top of bag. Place in oven at low temperature (300) for 6 to 8 hours, until tender. Cut meat and pull apart. Drain off juice for gravy.
Heat juice in pan, add Wondra to thicken, add salt, pepper, and season all to taste.