From the Riverford Farm Cook Book by Guy Watson and Jane Baxter. 'Dev' is for 'Devon'. Its delicious, and easy, despite the long ingredients list.
You really don't have to be too precious with how you do this. I have used a blender and a masher rather than a stick mixer - all works fine as long as your pumpkin is cooked enough. I've also added in potato and sweet potato if I'm low on pumpkin. It's all good.