1Cook beef and garlic powder in 10-inch skillet over medium heat, stirring occasionally, until beef is brown; drain. Stir in Potatoes, Sauce Mix, hot water and milk.
2Heat to boiling, stirring occasionally; reduce heat. Cover and simmer about 25 minutes, stirring occasionally, until potatoes are tender.
3Stir in mushrooms and sour cream; heat just until hot. Let stand 5 minutes before serving (sauce will thicken as it stands).