Douglas Harper's Etymology Dictionary
foie-gras
1818, French, short for pâté de foie gras (1827 in English), literally "pie of fat liver;" originally served in a pastry (as still in Alsace), the phrase now chiefly in English with reference to the filling. French foie "liver" is cognate with Italian fegato, from Latin *ficatum. For pâté see pate (n.2); for gras see grease (n.).