Preheat oven to 325°F. Spray a 9-inch springform pan with cooking spray and set aside.

In the bowl of an electric mixer, cream together cream cheese and sour cream until smooth, about 2 minutes. 

Gradually add sugar substitute and mix well. Add eggs, one at a time, beating until each is fully incorporated. Add lemon zest, juice, vanilla extract, and salt and mix until just combined. 

Pour into prepared pan and bake 1 hour to 1 hour 15 minutes or until center is almost set but still slightly jiggly. 

Let cool completely. Transfer to refrigerator and let set overnight.

Serve slices with a dollop of whipped topping and additional lemon zest.