In a medium pan, heat milk, sugar, pumpkin puree, pumpkin pie spice, and vanilla over medium heat.
Stir frequently until it simmers gently.
Let the mixture cool slightly, then stir in the heavy cream.
Cover and refrigerate until fully chilled.
Pour the chilled mixture into your ice cream maker and churn as per the instructions.
Transfer to a container, cover, and freeze until firm.
Serve with crushed graham cracker crumbs on top.