Prepare the Mushrooms - Rinse and dry the fresh mushrooms, or wipe the surface with a damp paper towel. Trim the stems and cut them into ¼-inch thick slices.
Cook the Aromatics - Heat a large pot or Dutch oven over medium-low heat. Add the butter. Once melted, add the onions. Saute until lightly brown and translucent, about 6 to 7 minutes. Add the minced garlic and thyme, and saute for 30 seconds.
Cook the Mushrooms - Increase the heat to medium. Add the sliced mushrooms and sprinkle with salt and pepper. Saute until tender and most of the moisture releases, occasionally stirring, about 6 to 7 minutes. Reserve a ¼ cup of for garnish.
Reduce the Liquids - Add the wine and vinegar, stir, and cook until most of the liquid evaporates about 3 to 4 minutes. Add the dried porcini mushrooms and stir to combine.
Simmer the Soup - Add the vegetable stock and bring to a boil over high heat. Reduce the heat to low, cover, and simmer until mushrooms are tender, about 15 minutes, stirring every five minutes.
Puree the Soup - Carefully transfer the soup to a countertop blender and reserve the pot. Cover to prevent splattering. Do not fill the blender more than halfway full; work in batches if needed. Puree on medium speed for 30 seconds. Increase to high speed, process until a smooth, about 1 minute. Transfer the pureed soup back to the pot.
Add the Cream - Heat the soup over low heat. Add the cream and stir to combine. Continue to stir and cook until hot, about 4 to 5 minutes. Season with salt and pepper to taste.
To Serve - Divide the soup among serving bowls. Garnish with reserved mushrooms and chives.
Notes
Recipe Yield: 4 cups
Serving Size: 1 cup
Storing: Cool soup completely. Store in an airtight container in the refrigerator for up to 5 days.
Reheating: Place soup in a pot over medium heat, adding more stock if needed, occasionally stirring until hot.
Vinegar Substitutes: Add balsamic vinegar, red wine vinegar, or apple cider vinegar.
Make it Dairy-Free and Vegan: Substitute extra-virgin olive oil for butter. Canned unsweetened coconut milk, cashew milk, or oat milk can be used instead of heavy whipping cream; add just enough until desired consistency is reached.
Wine Options: Use Chardonnay, Pinot Grigio, or Sauvignon Blanc. The wine can be omitted and substituted with more stock.