Mix together the cream cheese, lemon zest and vanilla until smooth. Stir in 1/2 cup sugar then beat in the eggs one at a time until blended.
Pour the cheesecake mixture into the pastry cases, being careful to distribute it evenly. Shake the pans gently to settle the batter then bake in the preheated oven for 25 minutes. Remove the cheesecakes, but do not turn off the oven. Allow cheesecakes to cool before topping.
For the sour cream topping: Whisk together the sour cream, 1/2 cup sugar and vanilla until blended. Distribute the topping mixture over the two cooled cheesecakes. Bake cheesecakes in the oven for an additional 10 minutes. Cool completely, then refrigerate until serving.