Heat 1 Tbsp. oil in Dutch oven over medium heat until hot. Brown beef with garlic in batches; pour off drippings. Return beef to pan; season with pepper. Stir in broth and thyme; bring to a boil. Reduce heat; cover tightly and simmer 1-3/4 to 2 hours or until beef is fork-tender. Meanwhile heat oven to 425°F. Place vegetables in lightly oiled jelly roll pan. Drizzle with 1-1/2 Tbsp. oil and vinegar; toss. Roast in 425°F oven 20 to 25 minutes or until tender. Stir cornstarch mixture into stew; cook and stir 2 minutes or until thickened. Stir in vegetables and 2 tsp. vinegar. Serve with couscous. Makes 6 servings.