Special equipment: 1 (8-inch) springform cake pan
Preheat oven to 400 degrees F.
Spray the springform pan with nonstick vegetable oil cooking spray. Set aside. In a shallow roasting pan big enough to fit the cake pan, pour about 1-inch of water and place it on the center rack of the oven to preheat.
In the bowl of an electric mixer, beat softened cream cheese, ricotta, sour cream and sugar substitute on low speed for about 1 minute until well blended.
In a separate bowl, using a wire whisk, mix heavy cream, vanilla, lemon juice, eggs, and egg yolks until blended.
Turn the mixer on medium speed, and slowly pour the egg mixture into the cream cheese mixture. Beat just until blended and then turn off; be careful not to over-whip.
Pour batter into the greased springform pan. Place pan into the heated water bath. Bake for 15 minutes, and then lower the oven temperature to 275 degrees F. Continue baking for 1 1/2 hours, or until top is light golden brown and cake is pulling away from the sides of the pan. Turn the oven off when finished cooking and leave the cake in the oven to cool for 3 more hours. (This will keep the cake nice and tall.) Then remove cake and refrigerate before serving. Serve chilled.