In a small bowl, whisk the eggs, sugar, cornstarch, and cake flour til smooth.
In a small saucepan, heat the milk til steamy and just beginning to simmer. Don't let the milk boil.
Temper the eggs by pouring the warm milk into the egg mixture. Constantly whisk the eggs while pouring the milk so you don't curdle the eggs.
Once the milk is fully incorporated into the egg mixture, return the eggs back into the pan. Gently whisk the custard constantly to avoid curdling. Heat the custard over medium low heat for about 5-7 minutes until the mixture thickens.
The custard will be done when it can easily coat the back of a spoon and a small trail gets left behind when you run your finger through the custard.
Pour the custard through a sieve to remove any lumps. Meanwhile, in a small microwave safe bowl or measuring cup, add the cream cheese and sour cream together. Heat on high for 15 seconds. If the mixture is still hard, it might need to be heated 15 more seconds. Whisk the cream cheese and sour cream to combine.
Fold the cream cheese mixture into the custard until it is fully incorporated.
Cover with plastic wrap and let the mixture chill in the fridge until it is fully set and ready to use.