Report Abuse. Perhaps you can trace its origin from the word itself. The word flan does indeed come from France where it was used to describe a custard tart or a cheesecake. It came from the Old French word flaon which, in turn comes from the Medieval Latin word fladu.The origins go back to Proto-Germanic flado.eport Abuse. Perhaps you can trace its origin from the word itself. The word flan does indeed come from France where it was used to describe a custard tart or a cheesecake. It came from the Old French word flaon which, in turn comes from the Medieval Latin word fladu.