Cook potatoes, covered, in boiling water 20 to 25 minutes or until tender; drain. Mash; set aside.
In a bowl combine bread crumbs, margarine, and parsley. Press mixture onto bottom and up sides of a lightly greased 1-1/2-quart casserole. In a bowl combine egg yolks, basil, lemon peel and juice, salt, and white pepper; stir in milk and 1 cup of the cheese. Stir milk mixture into mashed potatoes.
Beat egg white until stiff peaks form; fold into potato mixture. Transfer to prepared casserole; top with remaining cheese. Bake, uncovered, in a 350 degree F oven about 45 minutes or until knife inserted in center comes out clean. Garnish with snipped parsley. Makes 8 to 10 side-dish servings.