Clean mushrooms with a damp cloth, slice them evenly, then chop the onion and garlic so every ingredient cooks quickly and uniformly in the pot.
Heat butter and olive oil in a pot, add onion and garlic, and cook gently until softened, fragrant, and translucent, without allowing them to brown.
Add mushrooms, thyme, salt, and pepper, then cook over medium heat until released liquid evaporates and the edges begin to brown lightly around the sides.
Sprinkle flour over the mushrooms, stir for one minute, then gradually add vegetable stock while mixing continuously to prevent lumps from forming inside the soup.
Simmer the soup until the mushrooms are tender, blend until smooth, then return it to low heat and stir in cooking cream until fully combined.
Warm gently without boiling, adjust the seasoning, and serve with grated cheese, toasted bread, fresh thyme, and a small drizzle of olive oil on top.
