Place thoroughly washed greens on cutting board; using a sharp knife, cut greens into bite-size pieces. Place greens, shredded cabbage, and water in a large Dutch oven; bring to a boil. Reduce heat, cover and simmer 20 minutes. Remove greens mixture from Dutch oven and drain, reserving liquid. Set aside.
Melt shortening in a Dutch oven over medium heat; add ham hock, and cook until browned. Remove ham hock; set aside. Add greens mixture, onion, green onion tops, parsley, bay leaves, and thyme; cook over medium heat 3 minutes, stirring constantly. Stir in 2 tablespoons flour, salt, pepper, and hot sauce.
Add reserved ham hock and reserved liquid. Bring to a boil. Reduce heat, cover and simmer 1 hour.
Combine remaining flour and a small amount of water to form a smooth paste. Stir into greens mixture, and cook 1 minute.