Place the cream cheese in a microwave-safe bowl and warm it for 10 seconds. It should soften enough to stir easily without melting into liquid.
Stir in the sugar and vanilla extract until a thick paste forms. The goal is a smooth mixture that looks like frosting, with no visible cream cheese lumps.
In a separate measuring cup, combine the whole milk and heavy whipping cream, then add that liquid to the paste a little at a time while stirring. Starting slowly helps the sugar dissolve fully, and the finished base should feel smooth rather than gritty.
Pour the mixture into a Ninja Creami pint, cover it, and place it on a level spot in the freezer for 24 hours. A flat frozen surface helps the machine process the pint evenly and reduces the chance of an uneven spin.
Take the pint out, remove the lid, set it into the outer bowl, and lock the machine parts into place as directed for your model. The base should be frozen solid and level across the top.
Select the Ice Cream function and let the machine run for about 2 minutes. The machine will be loud, especially at the start, and that is completely normal.
Open the pint and check the texture before serving. If it looks smooth and silky and holds its shape on a spoon, it’s ready to eat. If it's crumbly, add 1 tablespoon of milk and run a re-spin.