Chop the beef liver into small pieces. Place in a bowl or freezer bag with soy sauce and Worcester sauce. Refrigerate for 30 minutes. After marinating, lightly coat with flour.
Heat clarified butter or vegetable oil in a large skillet over medium-high heat. Fry the liver pieces for 3-4 minutes, turning occasionally, until cooked through. Dust with pepper and paprika powder, then remove the liver and set aside. Do not season with salt yet, as salt will make the liver tough and dry.
In the same skillet over medium heat, cook the onion rings for 3-4 minutes until they start to soften. Season with salt and pepper.
Add red wine and broth (if using) to deglaze the pan, scraping up any browned bits. Return the liver to the skillet and add the cognac. Reduce heat to low and simmer gently for 30 minutes.