Drain and rinse the beans in cold water. Place 3/4 cup of them in a food processor with 1/4 cup of cold water and pulse until almost smooth. Heat the olive oil in a large skillet over medium heat. Add the pork and onion and cook until the pork is nicely browned, about 5 minutes. Add the garlic and cook 1 minute more. Add the stock, mashed and whole black beans, sausage and bay leaves and bring to a simmer. Gently simmer 30 minutes; season with salt and pepper. Serve on rice and garnish with sliced orange and cilantro sprigs, if desired.