why should the madeleine tins start off cold?
David Lebovitz tells us that chilling the tins prior to filling helps the cakes to develop a "humpy" appearance, particularly if baking powder is used (which some chefs say to NEVER use in Madeleines). Also, since the tins are usually prepared by brushing with melted butter mixed with flour, chilling would keep that where it belongs instead of it pooling in the bottom of the tin.