Preheat oven to 350°.
Combine first 8 ingredients in a large bowl; stir well. Spoon mixture into an 11- x 7-inch baking dish coated with cooking spray.
Heat milk in a medium saucepan over medium heat until very hot. (Do not boil.) Stir in potatoes; cook, stirring constantly, 5 minutes or until thickened. Stir in sour cream and 1/4 teaspoon salt.
Spread potato mixture over vegetable mixture; sprinkle with paprika. Spray top with cooking spray. Bake at 350° for 40 minutes or until top is lightly browned. Serve immediately.