In a small bowl, combine chocolate wafers and butter. Press onto the bottom of a 6-in. springform pan coated with cooking spray. Place on a baking sheet. Bake at 325° for 10 minutes. Cool on a wire rack.
In a large bowl, beat cream cheese and sugar until smooth. Add sour cream and flour; beat well. Add egg; beat on low speed just until combined. Stir in the lemon juice, peel and vanilla just until mixed. Pour over crust.
Return pan to baking sheet. Bake at 325° for 40-45 minutes or until center is almost set. Cool on a wire rack for 10 minutes. Carefully run a knife around edge of pan to loosen; cool 1 hour longer. Refrigerate overnight. Refrigerate leftovers.