8 ounces sliced mushrooms
1 tablespoon butter
1 to 1 1/4 pounds lean pork, cut in thin strips
1 medium onion, halved or quartered and thinly sliced
1/2 cup flour seasoned with 1/2 teaspoon salt, dash pepper, and 1/4 teaspoon paprika
2 tablespoons vegetable oil
1 can (14 ounces) cups beef broth
3 tablespoons tomato paste
1 teaspoon Worcestershire sauce
1 cup sour cream