In a small bowl, whisk cornstarch in ¼cup milk.
In a medium saucepan, combine pumpkin puree, remaining milk, heavy cream, vanilla extract, sugars and corn syrup. Mix well and bring to a boil on medium heat. Remove from heat.
Stir in the cornstarch mixture, whisking continuously. Cook on medium flame until the custard thickens significantly.
Remove the pan from the heat and let the custard cool to room temperature, stirring occasionally to prevent a skin from forming. Refrigerate for at least 2~3 hours or overnight.
Transfer the custard to an ice cream maker. Freeze according to the manufacturer's instructions. Serve immediately if you prefer soft, creamy ice cream. For firmer consistency, transfer the ice cream to an airtight container and freeze for about 2 hours.