Gemeente Museum ~ The Hague when I was last in the Netherlands a few months ago. I've tried to find it on their site or elsewhere online to find the title and when it was painted etc, but to no avail! And my picture here is not ideal, as the glass reflection undermines the luminosity and beauty of this work. I think it was quite an early piece, before his more famous works, which everyone knows off by heart.
I notice that there's an exhibition on at the Pompidou Centre in Paris, and there's an excellent little film clip about that here.
Its worth a visit if you're in Europe.