Prepare the vegetables and rosemary according to the ingredient amounts in the recipe card. Cut the potatoes into larger chunks, chop the celery and prepare the carrots as needed.
Add the flour and beef stew meat to a large resealable bag. Seal the bag and shake until the beef is evenly coated.
Heat half of the oil in a large skillet over medium-high heat. Brown half of the beef on all sides, then transfer it to the slow cooker. Add the remaining oil and repeat with the rest of the beef. During the final minute of browning, add the garlic and stir frequently so it cooks without burning.
Add the potatoes, carrots, celery, and pearl onions to the slow cooker with the beef. In a measuring cup or bowl, whisk together the McCormick Beef Stew Seasoning Mix and water until combined, then pour it over the beef and vegetables. Top with the fresh rosemary and stir gently to combine.
Cover and cook on low for 6 to 8 hours, or until the beef is tender and the vegetables are cooked through. If the gravy is thinner than you prefer, mix ¼ cup water with 2 tablespoons cornstarch and stir it into the stew during the final 20 minutes of cooking.