Combine canned pumpkin and 2 cups milk in a large saucepan. Cook over medium heat, stirring constantly until mixture begins to thicken and bubble (about 5 minutes)
Whisk in spices and sugar. Turn heat down to low, and continue to whisk frequently. Meanwhile, heat 3 cups milk in microwave until approximately 140 degrees Fahrenheit (60 Celsius).
Using an immersion blender, mix the hot milk (in a tall container, to prevent splatter) until frothy.
In a separate tall container, use immersion blender to whip the heavy whipping cream (should take 30 seconds or less).
Fill each mug 1/2 with pumpkin mixture and 1/2 with frothed milk. Add as much whipped cream as desired, and stir to combine. Top with cinnamon. Serve immediately.