Preheat oven to 400 degrees. Place potatoes in 9-inch glass pie plate and bake for 20 minutes. Remove, reduce oven to 350 degrees. Cool enough to mash potatoes into a thin crust on bottom and up sides of pie plate. Arrange sausage over crust, then top with 1 cup of cheese. Mix remaining ingredients and carefully pour into crust. Bake at 350 degrees for 25 to 30 minutes or until center is set. Sprinkle remaining 1/2 cup shredded cheese on top and let melt. Cut into wedges and serve.