In a large pan, melt butter in oil over medium heat. Cook meat until browned on all sides. Remove with slotted spoon to a warmed dish.
Place garlic, pepper and onion in remaining oil, and lightly fry until onion is translucent. Return meat to pan; lightly mix together. Stir in walnuts, and cook and stir for one minute. Stir in tomato juice, and season to taste with salt and pepper. Cover, and bring to a boil. Reduce heat, and simmer for 1 1/2 hours. Stir in mushrooms; cook for 20 minutes.