Cook - Heat oil in a large Dutch oven over medium heat. Add beef, pork, and chicken liver. Cook until browned and crisp, around 15 minutes. Add half of the chicken broth, scrape up browned bits from the bottom, and cook until evaporated. Repeat with remaining broth. Add onion, bell pepper, and celery. Cook until softened, about 5 minutes. Add garlic and stir until fragrant, about 1 minute.