Taste the soup and add more salt and pepper if needed. Add the heavy cream and nutmeg, then turn off the heat. Remove 1/4 cup of the sliced mushrooms for garnishing, then when the soup is no longer steaming (about 10 minutes), puree in batches in a blender. (Alternatively, you can puree in the pot with a stick blender.)
A few changes I've made from The Grape's version: I cut the recipe in half, and I added more thyme and garlic. I also reduced the amount of flour, and while I haven't made it without, I think it would still be fine if you care not to include flour. The original recipe also didn't call for a sliced-mushroom garnish, though I think it's prettier that way.
The Grape's mushroom soup | www.homesicktexan.com