Cover the beans with water by 2 inches and soak 8 hours or overnight. Drain.
Heat the bacon grease in a large pot over medium-high heat and cook the tasso 1 minute. Add the onions, celery and peppers, season with the salt, pepper and cayenne and cook until soft, about 4 minutes.
Add the bay leaves, parsley, thyme, sausage and ham hocks and cook to brown the meat, about 4 minutes. Add the garlic for 1 minute.
Add the beans and stock, bring to a boil, then simmer uncovered over medium-low, stirring occasionally, until tender and starting to thicken, about 2 hours. Add water 1/4 cup at a time if too thick.
Mash about a quarter of the beans against the side of the pot and cook until creamy, 15 to 20 minutes more. Remove the bay leaves and serve over rice with green onions.