In a large pot or Dutch oven, melt the butter over medium-low heat. Sauté the chopped onion and minced garlic until the onion turns translucent and the garlic becomes fragrant, which takes about 3-4 minutes.

Add the mushrooms into the pot and cook, stirring occasionally, until they release their moisture and start to brown, which takes about 5-7 minutes. You will know the moisture is released when there’s a layer of liquid on the bottom of the pot.

Evenly sprinkle the flour over the cooked mushrooms, stirring well to coat them. Cook for an additional minute to eliminate the raw flour taste.

Gradually pour in the chicken or vegetable broth while stirring constantly to prevent lumps. Bring the mixture to a boil, then reduce the heat to low and let it simmer for approximately 15 minutes to allow the flavors to develop.

Carefully blend the soup until it turns smooth and creamy using either an immersion blender or a regular blender. If using a regular blender, work in batches and exercise caution while working with the hot soup.

If needed, return the soup to the pot and stir in the heavy cream and dried thyme. Season with salt and pepper according to taste. Simmer for an additional 5 minutes to ensure thorough heating and melding of flavors.

Serve the creamy mushroom soup garnished with sautéed mushrooms, fresh parsley or thyme, and enjoy it while still hot.