I found the original recipe here at familyfun.com. I "kicked it up a notch" with the addition of pumpkin-pie flavoring syrup.
Mix 1/2 cup canned pumpkin, 3/4 cup whole milk, 1/4 teaspoon cinnamon, 1/8 teaspoon nutmeg, 1 tablespoon brown sugar, 2 tablespoons pumpkin-pie flavored syrup, and 4 to 6 ice cubes in a blender. Pour into 2 glasses. Top with a dollop of whipped topping if you so desire.