Peel the potatoes, carrots, shallots and garlic cloves.
Clean the leek, celery and mushrooms.
Finely chop the shallots.Slice the carrots and the white parts of the leeks into rounds, cut the potatoes into large cubes, and chop the celery stalk into small pieces.Trim the ends of the mushroom stems and cut them into quarters or halves. In a cast-iron casserole dish, heat the olive oil and add the sliced shallots, cooking until translucent.Then add the crushed garlic clove and the pink peppercorns. Pour over the white wine and fish/vegetable stock. Add the bay leaf and celery stalk.
Add the carrots and potatoes and cook for 10 minutes.Add the leeks and continue cooking for another 10 minutes.When all the vegetables are tender, remove them with a slotted spoon and transfer them to a salad bowl. Meanwhile, cook the mushrooms separately with butter, in a pan.