Pour over the foie gras a thin layer of melted duck fat to help it keep longer. Cover and refrigerate for a further 2 or 3 days, to let its flavour develop.
Remarks
It's a slightly disconcerting recipe, but at least there is no risk of seeing the liver melt during cooking due to a too hot oven...
Note that this does not give quite the same texture as oven-cooked liver. Difficult to describe this difference, maybe "a bit firmer".