1. In 5-quart Dutch oven over medium heat, in hot salad oil, cook cabbage, mushrooms, onion, salt, and sugar until vegetables are tender, about 20 minutes, stirring occasionally.
2. Preheat oven to 425°F. Prepare piecrust mix as label directs. Roll half of pastry into circle to line 12-inch pizza pan. Cut remaining pastry into four equal portions. With hands, roll each into an 18-inch-long strand; gently twist each 2 strands together to make a rope. Moisten edge of pastry in pizza pan with water; top with pastry rope, pressing gently in place. Bake piecrust 10 minutes or until lightly browned.
3. Stir sour cream into cabbage mixture; spoon mixture into piecrust. Bake 10 minutes longer or until crust is golden brown and pie is hot.