Heat 2 tablespoons of olive oil in your large pot over medium heat. Once shimmering, add the chopped onion. Cook, stirring occasionally, until the onion is translucent and soft, about 5-7 minutes. Add the minced garlic and sauté for another 1-2 minutes until fragrant but not browned.
Add the sliced mushrooms to the pot. Stir to combine with the onions and garlic. Cook for about 8-10 minutes, stirring occasionally, until the mushrooms release their moisture and begin to brown.
Pour in 4 cups of vegetable broth and sprinkle in 1 teaspoon of dried thyme. Stir everything together, bring the mixture to a boil, then reduce heat and let it simmer gently for 15 minutes.
Use an immersion blender directly in the pot to puree the soup until smooth but still a bit textured. If using a countertop blender, carefully transfer soup in batches and pulse until desired consistency is reached.
Return blended soup to the pot if needed. Stir in 1 cup of heavy cream, then season with salt and pepper to taste. Warm the soup over low heat, avoiding boiling after adding cream.
Ladle soup into bowls and garnish with fresh thyme sprigs. Serve with crusty bread or alongside your favorite light meal.
