Preheat the oven to 350 degrees F. Bring a large pot of water to boil. Add cabbage leaves and cook until just tender, about 2-3 minutes. Cool in cold water, drain well and pat dry, Trim centre rib of each leaf if tough, and then set aside. Combine the beef, rice, egg, onion, garlic, thyme, salt and pepper in a bowl. Divide and place beef mixture in the centre of each cabbage leaf. Fold over sides and then tightly roll. Place cabbage rolls in a casserole. Pour over diluted soup. Cover and bake 90 minutes.