Heat oven to 425°F. Spray 9-inch deep-dish glass pie pan with nonstick cooking spray. Cook sausage in large skillet over medium-high heat until thoroughly cooked, stirring frequently. Drain.
Add potatoes and onion to sausage in skillet; mix well. Cook 5 to 8 minutes or until potatoes are slightly soft, stirring occasionally. Remove from heat. Stir in cheese.
Beat eggs in large bowl. Add milk; blend well. Reserve 1 tablespoon egg mixture for topping. Add potato mixture to remaining egg mixture; mix well. Spoon potato-egg mixture into sprayed pie pan, keeping mixture away from edges.
Remove pie crust from pouch. Unfold pie crust; press out fold lines. Place over potato mixture, tucking edges of crust around potato mixture. Turn edges under and press to edge of pie pan. Cut several slits in crust for steam to escape. Brush with reserved tablespoon egg mixture.
Bake at 425°F. for 25 minutes. Cover top of pie with foil to prevent excessive browning. Bake an additional 15 to 20 minutes or until potatoes are tender and crust is deep golden brown. To serve, cut into wedges.