Preheat the oven to 400 degrees F.
Line a baking sheet with parchment paper or foil.
Add the mushrooms to the baking sheet and drizzle with the olive oil and garlic, tossing well so the mushrooms are mostly coated.
Sprinkle the mushrooms with salt and pepper.
Roast the mushrooms in the preheated oven for 25-30 minutes, until browned and tender.
While the mushrooms are roasting, make the rest of the soup. Add the butter to a soup pot over medium-high heat.
Add the diced shallots to the melted butter and cook until softened, about 5-7 minutes.
Add the flour and stir until combined. Cook for 1 minute, until slightly browned.
Slowly stir in 1/2 cup of chicken/vegetable broth and scrape up any browned bits from the bottom.
Slowly add the rest of the chicken/vegetable broth, whisking as you add it to create a creamy soup base.
Once it is all added bring the soup to a boil, reduce the heat to medium-low and simmer for about 15 minutes.
Add the roasted mushrooms, stirring to combine.
Remove 2 cups of the soup, including some of the mushrooms, and puree in a high-speed blender. Return the puree to the soup and stir to combine.
Stir in the heavy cream and cook for another 1-2 minutes, until it is warmed through.
Serve topped with fresh thyme. Enjoy!