How to Make It
Heat the oil in a large saucepan. Add the chicken wings and beef and cook over moderately high heat until browned all over, about 10 minutes. Season with salt and pepper and add the carrots, onion, celery root and tomato. Cook over moderate heat, stirring occasionally, until the vegetables are barely softened, about 10 minutes.
Add the broth to the pan and bring to a boil. Cover partially and cook over moderately low heat for 30 minutes. Strain the stock, reserving the meat and vegetables for another use. Refrigerate the stock and remove the fat from the surface before using or freezing.