Cut up the kabocha squash with the skin on, take out the seeds and pulpy insides and line the cut up pieces on a heatproof dish. Add 50 ml of water, and cover loosely with plastic wrap.
Microwave for 10 minutes at 700 W. When the kabocha squash is tender, leave for about 20 minutes to cool down.
When the kabocha squash has cooled down enough to touch, use a spoon to remove the insides from the skin.
Heat the butter in a pan and saute the sliced onion. When the onion is translucent, add 50 ml of water and the soup stock cubes, and heat.
Put the contents of the pan in the food processor. Add some of the cooked kabocha squash too and process to a paste.
Return the contents of the food processor to the pan. Add the remaining kabocha squash, and add the milk a little at a time, stirring constantly and heating.
When the soup has reached the consistency you like, season with salt and pepper. Chill well in the refrigerator. Serve topped with cream or parsley.
Some kabocha squash may be a bit dry. If the kabocha squash doesn't blend well with the milk, pass it through a fine meshed sieve first.
Return the kabocha squash stuck on the sieve to the pan, and simmer while adding some cream to make it smooth. Then add the rest of the sieved squash and mix well.
Story Behind this Recipe
My family loves soup. Simmered kabocha squash isn't too popular, but turn it into soup and it's gone in the twinkle of an eye. I make this recipe without hesitation whenever I have a lot of kabocha squash.
If you put the piping hot onion soup in the food processor it may explode, so process in batches. If you like the soup to be really smooth, I recommend processing all the soup.