Combine wafer crumbs and butter, mixing well.
Press mixture into bottom of a 9-inch spring form pan; set aside.
Beat cream cheese at low speed of an electric mixer until light and fluffy; gradually add 3/4 cup sugar and 1/2 cup sour cream, mixing well.
Add eggs, one at a time, beating well after each addition.
Stir in 1 teaspoon vanilla and 1 package chocolate morsels.
Spoon into prepared pan.
Bake at 325° for 1 hour.
Cool at room temperature on a wire rack for 20 minutes.
Combine remaining sour cream, 1/2 cup sugar, lemon juice, and 1 1/2 teaspoons vanilla, mixing well; gently spread over top of cheesecake.
Bake at 475° for 5 minutes.
Cool to room temperature on a wire rack; refrigerate 8 hours.
Remove sides of spring form pan; sprinkle additional chocolate morsels around top edge and in center of cheesecake, if desired.