In food processor with knife blade attached or in blender at medium speed, blend vanilla wafers until fine crumbs form. (You should have about 1 cup crumbs.)
Preheat oven to 375°F.
In small saucepan, melt margarine or butter over low heat; stir in 1 teaspoon lemon peel.
In 9" by 3" springform pan, with fork, stir wafer crumbs and melted margarine mixture until moistened.
With hand, press mixture firmly onto bottom of pan.
Bake crust 10 minutes.
Cool completely in pan on wire rack, about 30 minutes.
Wrap outside of pan with foil.
Turn oven control to 325°F.
In cup, combine sugar and cornstarch until blended.
In large bowl, with mixer at medium speed, beat cream cheese and ricotta cheese until smooth, about 5 minutes; slowly beat in sugar mixture.
At low speed, beat in eggs, half and half, lemon juice, vanilla, and remaining 3 teaspoons lemon peel just until blended, scraping bowl often with rubber spatula.
Pour cream cheese mixture onto crust.
Bake cheesecake 1 hour and 15 minutes.
Turn off oven; let cheesecake remain in oven 1 hour longer.
Remove cheesecake from oven.
Cool completely in pan on wire rack.
Cover and refrigerate cheesecake at least 6 hours or overnight until well chilled.
Remove side of pan to serve.
Garnish with lemon peel and mint sprigs.