Sounds a great easy cooling idea. What size tray did you find suitable? I have a couple of large pizza trays that might do the job -- theyre pretty wide -- 37 cm diameter.
Ive just started making espresso from my first corretto roast and its sensational. Sure beats my old hand-stirring heatgun method!
Next step will be to find a cheap temperature probe ... just to make perfection a tad more perfect..