Heat olive oil and butter in a large pot over medium heat. Sauté onions and garlic until softened, about 3 minutes.

Add mushrooms and cook until tender and golden, about 8 minutes.

Sprinkle flour over the mushrooms, stirring for 1-2 minutes to cook the flour.

Slowly add stock, stirring constantly, and bring to a gentle simmer.

Reduce heat and cook for 15 minutes, allowing flavors to meld.

Blend the soup using an immersion blender until smooth (or leave slightly chunky if preferred).

Stir in cream and sherry, simmer for another 5 minutes.

Season with salt and pepper to taste, and garnish with thyme before serving.