Cozy Up with Hearty Slow Cooker Beef Stew

F0r the Beef: – 2 pounds lean beef chuck, cut into 1 1/2-2-inch pieces – 1/3 cup all-purpose flour – 1/2 teaspoon salt – 1/4 teaspoon black pepper – 1 tablespoon olive oil Vegetables: – 1 (16-ounce) bag of frozen pearl onions or 1 onion chopped – 2 large potatoes, peeled and cubed – 2 carrots, chopped – 2 celery stalks, chopped – 2 cloves garlic, minced Sauce: – 1 (28-ounce) can crushed tomatoes – 1 cup beef broth – 1 teaspoon salt – 1/2 teaspoon black pepper – 1 teaspoon dried thyme – 1 teaspoon dried rosemary – 1 teaspoon dried oregano – 1 bay leaf  For Thickening the Sauce: – 1 tablespoon cornstarch – 2 tablespoon water