In a large skillet over medium-high heat, brown the ground beef with the diced onion until beef is no longer pink, then drain excess fat.
Stir in minced garlic and cook for 1 minute until fragrant.
In a bowl, whisk together the cream of mushroom soup, beef broth, salt, pepper, and dried thyme.
Grease the slow cooker crock and layer half of the potatoes, half of the beef, and 1 cup of cheese.
Repeat layers with remaining potatoes and beef.
Pour the soup mixture evenly over the top layer.
Cover and cook on High for 4 hours or Low for 7 hours until potatoes are fork-tender.
Sprinkle remaining cheese over the top 15 minutes before serving.