In a small bowl, mix cornstarch and 1/4 cup milk to prepare cornstarch slurry. In a large bowl, whisk cream cheese until smooth. Set both bowls aside.
Prepare Pumpkin Mixture. Combine pumpkin, brown sugar, corn syrup & spices in a small saucepan. Cook, stirring periodically, until sugar dissolves and mixture starts to bubble, then remove from heat.
Prepare Ice Cream Base. Combine skim milk, salt, cream sugar and corn syrup in a large sauce pan. Bring to a boil and cook for 4 minutes. (Watch carefully so it doesn't boil over.)
Remove ice cream base from heat, stir in cornstarch slurry and pumpkin puree then return to heat, cooking for another minute or two until thickened.
Gradually add a little of the warm mixture to the softened cream cheese, whisking until you have a smooth mixture that can be combined with the remaining base without lumping. Mix in rum if using.
Chill until cool. (I usually chill an hour or two in the freezer, stirring periodically. Cooling in a zip loc bag in ice water or in the refrigerator are also options). Freeze according to your machine’s directions.
I am not a health professional and nutrition data is calculated programatically. Accuracy may vary with product selection, calculator accuracy, etc. Consult a professional for the best information.