Pumpkin is a beautiful and generous thing, and makes a sauce with a versatility approaching tomato sauce. If I said that in front of my family, whose pumpkin techniques are limited quite strictly to casseroles or frittelle, I don't know whether they'd laugh or smack me one, but I do feel it's true. While tomato sauce can give you degrees of what I consider a feminine sharpness, acidity, and clarity, running the gamut from invigorating to heartburn, pumpkin sauce gives you a gamut I imagine as masculine, from strongly comforting and fortifying to stolid.
I suppose if God held a gun to my head and told me to choose, I'd choose tomato; pasta in tomato sauce is my eternal comfort food, and I don't think the world has ever come up with anything lacking animal flesh in it that's quite as good as gazpacho. But I'd miss the pumpkin fiercely, and part of that is because the truth is a tomato sauce or gazpacho can be ruined, while a pumpkin sauce can be poor in relation to other pumpkin sauces but it will seldom be a disaster - unless you simply don't like it.
Here's the process, it's basically the same as the process for pumpkin soup, and applies to most varieties of pumpkin I've came across.
1. Fry your base (onions, garlic, the white part of leeks, celery, maybe some seedy herbs, like cumin or coriander seeds, or peppercorns, or whatever your taste runs to). Pumpkin takes kindly to a base fried in butter if you're not averse to heavier flavours.
2a. Once the base is sizzling enthusiastically add chunks of peeled, diced pumpkin and fry them for awhile (do yourself a favour and bake the pumpkin for ten minutes ahead of time, and then the skin lifts off quite easily with a normal veggie peeler.)
2b.You also have the option of splitting the pumpkin down the middle, roasting it at high heat face-down in an oiled tray, and then scooping out the cooked flesh after about half an hour. I like doing that because I think it makes it rather sweeter, but it depends on your tastes; it also tends to make it heavier.
3. Once the chunks have fried for awhile, or immediately if you have used roasted pumpkin flesh, add water or something else wet, translucent and inoffensive, just enough to cover. Anything from a rich meat broth through a veg broth back to water. Once again it's a question of your tastes.
4a. If you have used raw pumpkin chunks, cover and boil at medium heat until the chunks are tender, and puree - then you're fundamentally done.
4b. If you have used roasted pumpkin, you can puree immediately, but I suggest leaving it on low heat for ten minutes or so to make sure it's all melded, if that makes sense.
And there you go. More liquid gets you a pumpkin soup, less gets you a highly goopy sauce that is very nice for pizzas, especially paired with stinky cheese. Whether soup or sauce, this base also takes very kindly to the addition of curry paste to taste. It is also lovely with roasted red pepper pureed into it towards the end of the cooking; you can stick one or two in to roast at the same time as the pumpkin halves, if you go the roasting route. Green herbs should go in at the end, after removing it from the heat.
It also takes well to the addition of cheese, but to avoid clumps and ugliness mix in the cheese in the form of a bechamel-based cheese sauce.
As a soup, it works well either on its own or with the addition of other features, like (pre-cooked!) chick peas, or chunks of potato, shrimp, or white fish cooked directly in it. During this last shitty winter, I made a big batch of it every other week, in alternation with tomato sauce, and then froze it in jars that were just big enough to serve as a base for a quick but hearty and delicious soup for two in the evenings, so long as one or the other of us remembered to take out a jar to defrost in the mornings.
Finally it can be enriched either with cream out of cows or goats, or with milk out of coconuts. In either case it should be added after the soup or sauce has been pureed and taken off the heat, or, if you freeze it in batches, after it has been defrosted and re-heated.