Sauté the foie gras in half the butter for 1 minute on each side. Remove and set aside to rest.
Sauté the shallot in the remaining butter without colouring. Add the ceps or porcini and gently sauté for a further 10 minutes over a low heat.
Add the white wine and deglaze the pan, reducing the liquid to half over a low heat. Add the stock and again reduce the liquid to half.