Pot au Crème vs. Pot de Crème which is correct?

Well, I've seen both used in the same sentence interchangeably. My Spanish tells me that Pot au Crème would be cream in a pot or pot of cream and Pot de Crème would be a pot of creme but then Pot de Crème au Chocolate is a pot of cream with chocolate or a pot of chocolate cream.

So gentle readers, especially those that don't comment, which is it? Both?

I say both.