Soak kidney beans in cold water overnight. Water should be at least 2 inches over the beans.
Heat a large Dutch oven until hot. Pour in the oil and heat until it shimmers. Brown the smoked sausage and set aside.
Add a little more oil to the bottom of the pan, if necessary, and over medium heat sweat onion, celery and green pepper until onions are translucent.
Add the bay leaf and a heavy pinch of salt, pepper and Cajun seasoning. Cook until onions start to color.
Add the optional beer or about one cup of chicken or vegetable stock. Stir and cook to scrape off any bits stuck to the bottom of the Dutch oven.
Add enough stock to cover the beans by about 1 ½ inches.
Add several shakes of hot sauce and bring to a simmer. Simmer gently, uncovered, for about an hour. Add more liquid and turn down the heat if the liquid is reducing too quickly.
Taste, and adjust seasonings. Return the smoked sausage to the beans and cook an additional 20 minutes, or until the beans are soft
Mash some of the beans against the side of the pot to break them up and thicken the mixture.
Taste again, and add more seasonings or hot sauce, as needed. Remove bay leaves.
Serve over hot cooked rice. White is traditional, but brown rice adds a little more interest and fiber.