Painter's image in small reflective surface?

Could someone for the love of God please help me remember which painting was it that contained a very detailed small reflective surface (like an earring or something) in which the painter painted his own image? I mean, you know, it's something like velasquez's las meninas, only it wasn't a mirror, it was something significantly smaller (i suspect it's an earring). Anyway, it's a painting with a very high level of detail