Combine the cream cheese, butter and heavy cream in a mixing bowl and melt over a pot of lightly boiling water.

Beat the three chilled egg whites in a clean mixing bowl until the egg whites begin to foam. Slowly add in the sugar substitute as you continue beating at high speed. Add in the cream tartar and whip the mixture until stiff peaks are formed. Then prep the springform pan by lining it with parchment paper and then wrapping the exterior in large sheet of aluminum foil.

Add the egg yolks one at a time to the cream cheese mixture stirring constantly as you add the yolks. Then fold in the merengue. Only stir until the egg whites are incorporated into the cream cheese mixture. Then pour the mixture into the prepped springform pan. Place the foil wrapped pan into a baking dish or large casserole and add an inch of water into around the edge of the foil-wrapped pan.

Put the baking pan with the filled springform pan inside into the oven, middle rack, and bake at 280°F (140°C) for about 90 minutes until the top is lightly browned. Turn off the oven. Carefully remove the baking pan from the oven, remove the cake from the baking dish, remove the foil and carefully place the cake in the springform pan back into the oven while it cools down. Remove it after one hour resting in the oven. Then refrigerate for at least six hours before serving.