If using dried beans, sort through them to remove any small stones or debris. Place the beans in a large bowl and add water to cover. Soak overnight. Or place the beans in a large pot of water and bring to a boil over high heat. Once the beans come to a boil, remove from the heat and set aside for 1 hour. Before cooking, discard any floating beans and drain. Combine the soaked beans and fresh water to cover in a large, heavy-bottomed Dutch oven. Season with salt and pepper. Bring to a boil over medium-high heat, then decrease the heat to low. Simmer, covered, until the beans are tender, about 1 hour. Taste and adjust the seasoning with salt and black pepper. Set aside.
Heat a large heavy pot over medium heat. Add the sausage, beef and onions. Cook, stirring often, breaking up the meat, until no longer pink, 5 to 7 minutes. Add the garlic and jalapeno and cook until fragrant, 45 to 60 seconds. Add the chili powder, cumin, tomatoes and stock. Season with salt and black pepper. Bring to a boil over high heat then reduce the heat to simmer. Cook, stirring occasionally, until slightly thickened, about 30 minutes. Add the cornmeal and reserved cooked or canned and drained black beans and stir to combine. Cook, stirring occasionally, until thickened and the flavors have married, about 15 minutes. Taste and adjust the seasoning with salt and black pepper. Serve the chili with sour cream, green onions and hot sauce on the side.