Finely chop the onions and celery.

Melt the butter in a heavy-based pan over low heat.

Add the onions and celery to the pan and sauté for about 5 minutes, or until softened and translucent.

Chop the wild mushrooms according to preference.

Add the mushrooms to the pan and fry for 3-4 minutes, until they release their juices.

Stir in the dried herbs and basil.

Stir in the flour, ensuring there are no lumps. Cook for 1 minute.

Gradually add the vegetable stock and seasoning (salt and pepper).

Simmer for 8-10 minutes, until the sauce has thickened.

Remove the pan from the heat and stir in the sour cream or yogurt.

Taste and adjust seasoning as needed.

Return the pan to the stovetop and gently heat through to serving temperature, being careful not to boil.

Serve immediately on warmed plates.