Place the beef stew meat in the slow cooker. Add the cubed potatoes, sliced carrots, and thinly sliced onions on top.
In a small bowl, whisk together the beef broth, Worcestershire sauce, minced garlic, dried thyme, salt, and pepper. Pour the mixture over the meat and vegetables.
Cover and cook on low for 7 to 8 hours until the beef is tender and the vegetables are soft.
In the last 30 minutes, whisk the heavy cream with the cornstarch until smooth. Stir the mixture into the stew and continue cooking until the broth thickens slightly.