In a small bowl, whisk brown sugar, 1/4 cup water, vinegar, rosemary, garlic and soy sauce; set aside. Select saute or browning setting on a 6-qt. electric pressure cooker. Adjust for medium heat; add oil. When oil is hot, brown pork in batches. Press cancel. Return all pork and vinegar mixture to pressure cooker.
Lock lid; close pressure-release valve. Adjust to pressure-cook on high for 20 minutes. Let pressure release naturally. Remove pork to a serving platter. In a small bowl, whisk cornstarch and remaining 2 tablespoons water until smooth; stir into pressure cooker. Select saute setting and adjust for low heat. Simmer, stirring constantly, until thickened, 3-5 minutes. Drizzle over pork. If desired, sprinkle with additional rosemary.