Preheat oven to 180 degrees C. Bring a large saucepan of lightly salted water to a boil. Add pasta and cook for 8 to 10 minutes or until al dente; drain.
Place beef mince in a large, deep frypan. Cook over medium high heat until evenly brown and crumbled. Drain, excess oil and set aside.
Heat oil in a large heavy frypan over medium heat. Saute onion until soft and translucent. Stir in garlic and cook for 30 seconds. Add cooked beef, tomatoes, spaghetti sauce and mushrooms. Bring to a boil. Reduce heat and simmer 20 minutes.
In a casserole dish layer 1/2 of the pasta, 1/2 of the meat sauce, 1/2 of the sour cream and 1/2 of the grated cheese. Repeat layers.