While the pumpkin is cooking, get everything else ready.
In a medium bowl, mix the arrowroot with the oat milk until dissolved.
Add all the other ingredients and blend it well with an immersion blender (or a mixer).
It will be about the texture of a cream soup.
Ladle the puree into 8 greased ½-cup ramekins.
Bake in the oven at 350F degrees in a water bath for about one hour, until the pudding is thick and doesn't jiggle when you touch it. The top will be a nice, golden brown.
Notes
While you can use a carving pumpkin, the best pumpkin for this recipe is the pie pumpkin: it'll be sweeter and blend into a much smoother pudding.
To make a water bath, set the ramekins in a cake pan or another pan with a 3-inch side. Pour hot water into the pan, surrounding the ramekins, but about 1 inch or so below the top of the ramekin.