"Les expressions françaises décortiquées" [etymology of French expressions] (in French). expressio.fr. Retrieved 14 May 2015. Dating to the Middle Ages, adding butter to ones plate came to mean to "s'en mettre plein les poches" ["line ones pockets"]
Dixmier, Élisabeth; Dixmier, Michel (1974). L'Assiette au Beurre: revue satirique illustrée, 1901-1912 (in French). Paris: François Maspero. OCLC1432619.