Warm the oil in a large pot and add the celeriac, potatoes, leek, onions and shallots. Cook for 10 minutes over medium heat, stirring every once in a while. Add the vegetable stock and bay leaf, season with salt and pepper, and bring to a boil.

Reduce heat, then cover and simmer over low heat until the vegetables are tender, 15 to 20 minutes. Add the milk, stir well, and cook for another 5 minutes. Serve, placing a warm toasted baguette slice on top of each bowl.

Note: The traditional recipe calls for croutons, bread pieces fried in oil. We find leftover toasted baguette much lighter and just as delicious.