1. Preheat oven to 300 degrees F (150 degrees C).
2. Trim and discard extra fat on roast. Peel and cut potatoes into 6 chunks. Cut onion into 8 pieces. Cut carrots into 1 inch pieces. Cut celery into 1 inch pieces.
3. Place roast in a large baking pan; arrange potatoes, onion, carrots, and celery around roast. Pour 3 cups water into baking pan. Season roast with salt, pepper, and garlic salt. Cover pan with aluminum foil.
4. Bake in the preheated oven until roast is browned and cooked through, about 3 hours. An instant-read thermometer inserted in the thickest part of the roast should read 145 degrees F (65 degrees C). Transfer roast to an oven-safe platter. Remove vegetables using a slotted spoon and arrange around roast.
5. Reduce oven temperature to 200 degrees F (95 degrees C). Place platter with roast and vegetables in the oven to keep warm.
6. Pour the remaining juices from the baking pan into a saucepan; bring to a boil. Stir 1/2 cup water and cornstarch together in a bowl until smooth; pour into boiling pan juices. Reduce heat to medium; cook, stirring constantly, until gravy is thick, about 5 minutes; season with salt and pepper. Stir in browning sauce.