Foil over cookie sheet over broiling pan?
It's possible that the recipe author was going for insulation from the heat of the oven's element/flames on the bottom.  This would give you more cooking by convection - or baking without the browning on the bottom (conduction) where the food touched the thin pan.

Another way around this is insulated baking sheets - two layers with air in the middle.  On cookies, they take longer and reduce browning.  So this seems to me to be an approach to the insulated baking sheet, creating a workaround on the assumption that people have the other equipment at hand.