If you don't have a pressure cooker, no worries, you can do it stovetop- just cover over medium heat until the squash is very tender.
2 TB butter
3 cloves garlic
1 medium sweet onion, diced
2 lbs Banana Squash, peeled and cubed
1 good sized granny smith (or other tart apple) , cored and diced
1 medium sweet potato (white flesh is my preference), peeled and diced
4 cups chicken broth
1 TB dried basil
1 TB dried tarragon
salt and pepper to taste
red pepper flakes to taste
2 cups milk, half and half or heavy cream *depending on your creaminess desires, you could use a combo blend of fat content or whatever you like, I used whole milk.
Set your pot to saute, add butter, onion and garlic and cook until they are tender and fragrant.
Add squash, apple, sweet potato, and seasonings.
Set pot to Soup/Stew setting and set the timer to 20 minutes, close pot and GO.
When it is done, do the quick release.
Use an immersion blender or transfer it to a high speed blender in batches to puree to smooth.
Stir in milk/cream slowly. Adjust seasonings to taste and serve!