In a medium size pan over medium heat, bring milk, sugar, pumpkin puree, pumpkin pie spice, and vanilla extract to a low simmer, stirring frequently.
Allow the mixture to cool slightly, then add heavy cream. Cover and refrigerate until well chilled.
Pour the chilled mixture into the well of your ice cream maker, and churn according to the directions. Pour the ice cream into a container, cover, and freeze until firm. Serve with crushed graham cracker crumbs as a topping.