I just polished off a bowl of this I prepared Wednesday for a pot luck dinner with friends.
This is good with any kind of hard squash, including pumpkins. I've been making it for years. With a pressure cooker and a blender I can have it ready to serve in 1 hour from starting. I have a 5 liter Kuhn Rikon pressure cooker; when it's loosely filled with squash chunks I can make enough soup for 4 people, all of whom take seconds. That's one typical Kabocha, one small butternut squash, parts of a pumpkin or another larger squash. The beauty of the recipe is the squash and broth proportions are roughly 50:50 so you can make it with any size squash.
Winter squash
Broth - I use vegetable
Spices (see later)
Heavy cream (coconut cream works well for vegans)
Salt and pepper
Herbs for topping appropriate to the spices used
Cut the squash into chunks and remove seeds. Don't waste time peeling it. Steam, pressure cook or roast until soft. For a Kabocha I cut it into 8 pieces and pressure cook on the high setting for 4 minutes, then let it release naturally. Butternut squash takes 8 minutes at high pressure.
Let cool until you can handle it. Scoop the cooked flesh out of the shells into a large measuring cup. Pack it down, and add a little more than an equal volume of broth.
Either:Put the mixture into a pot. Use an immersion blender or hand mixer to puree the mixture. Add more broth or water to get the consistency you want. Add spices and heat to boiling. Turn down heat and simmer a little.
Or,Put the mixture into a blender. Add more broth or water to get the consistency you want. Add the spices. If you have a VitaMix blender, use the Heated Soups setting until its hot. Otherwise, after blending, put in a pot and heat to boiling. Turn down heat and simmer a little.
Add heavy cream to taste. I use about a cup / 225ml. Bring almost to the boil. Adjust seasoning with salt and pepper.
You can serve it hot or chill it for eating as a cold soup.
Serve topped with chopped herbs.
Spices:
I've tried these combinations of spices in the soup and herb toppings:
Sage topped with chives
Sage, thyme, rosemary topped with chives or parsley
Curry powder topped with finely shredded hot chiles, dried chile flakes, sweet or smoked paprika, or with chives
Cumin powder and diced garlic topped with cilantro (Chinese parsley) or chipotle chile powder
I don't like sickly sweet food so I stay away from combinations like maple syrup and nutmeg or allspice, but that would probably be good if you like that sort of thing.
As a variation you can broil the squash until it's caramelized on top. I have done this with squash I first pressure cooked, scooped out, mashed and spread on a layer of foil in a broiler pan. It takes quite a bit of time and constant attention, but the flavor is very good.
Finally, if you're in a hurry or are cooking for your in-laws, you can used canned pumpkin.