Add the milk, pumpkin puree, pumpkin pie spice, and vanilla ice cream (in that order) to a blender.
Blend on high or set on the puree setting for 30 seconds, or until combined and well-blended. *If the ice cream stops blending, stop the blender and stir the mixture with a spoon or spatula, then start the blender up again.
Divide the milkshake between two chilled 16-ounce glasses. If desired, top with whipped cream and graham cracker crumbs.
Notes
Feel free to add more pumpkin puree to the mix if you’d like more pumpkin flavor, but I feel that 1/2 a cup is just right.This is a customizable recipe! Taste as you go and add more or less of the spice, pumpkin puree, and/or milk to get the right combination for your taste.