In a large pot, heat the unsalted butter and olive oil over medium heat until melted.

Add the chopped onion and sauté for about 5 minutes until translucent and softened.

Stir in the minced garlic and sliced mushrooms, cooking for another 7-10 minutes until the mushrooms have released their moisture and are lightly browned.

Sprinkle in the dried thyme, stirring to combine, and cook for an additional minute to release the herb's aroma.

Pour in the vegetable broth, bring the mixture to a gentle boil, then reduce the heat and let it simmer for 15 minutes, allowing the flavors to meld.

Using an immersion blender, puree the soup until smooth. If you prefer a chunkier texture, reserve a portion of the mushroom mixture before blending.

Stir in the heavy cream and season with salt and pepper to taste. Heat through for an additional 5 minutes, but do not let it boil.

Ladle the bisque into bowls and garnish with freshly chopped parsley before serving.