Heat olive oil in a large pot over medium heat.
Add chopped onions and sauté until translucent.
Stir in minced garlic and cook for an additional minute.
Add the sliced mushrooms and cook until they release their moisture.
Sprinkle in the thyme, salt, and pepper.
Pour in the vegetable broth and bring to a boil.
Reduce heat and simmer for 15 minutes.
Use an immersion blender to puree the soup until smooth.
Stir in the heavy cream and heat through.
Serve hot, garnished with fresh parsley.