Melt the butter over medium heat in a soup pan or really big saucepan.
Cook onions/shallots until they are translucent- about 3-4 minutes. If you're using celery and/or carrots in your base, this is where you'd add them in too!
Turn heat down a little, add in the mushrooms abnd cook them down until soft and fragrant. This is where you would add in your "main" ingredient if it was hard- like broccoli, cauliflower, potatoes, etc..
Add in the garlic and any fresh herbs if you want to use those. Stir for 1 minute.
Add in the broth and coconut milk, simmer for 10 minutes.
Dump in the cashews, simmer for 5 more minutes. They will get nice and soft and will thicken the soup, like flour or a roux would.
Turn off heat and pull out about 1/2 cup of the mushrooms- set aside.
Use an immersion blender to cream the soup how you like it. Or, you can dump it into a Vitamix and blend but, um, I never do this because I spill. :/
Chop the resered mushrooms an dadd them back in- this gives some nice texture, like the canned soup has. This step would be yummy with celery or something, but I don't think broccoli. Ha ha.
If you're making a soup that needs cheese or "cheese-like," add in shredded cheese here or, for a non-dairy cheesy taste, a couple Tablespoons of Nutritional Yeast.