Brown all sides of the roast in a hot cast iron skillet.
Add oil to InstantPot and sauté diced onion. Once onion is softened add garlic, soy sauce, salt, pepper and browned roast. Add water to the cast iron skillet and scrape the fond (cooked bits) off the bottom. Pour into the InstantPot, seal and cook for 1 hour.
Remove meat to cool, then slice or shred. Meanwhile, strain the broth and discard the solids. Taste. If it seems weak pour it into a pan and simmer over the stove to reduce the liquid and concentrate the flavor. Salt to taste. Place the meat on toasted buns. Serve the sandwiches with hot broth for dipping. Makes about 6 sandwiches.
