Hi Susie! This is something PJ addressed in the article. The popovers should probably be the last thing you make as they really need to be served immediately. The article says: "As soon as they emerge from the oven they start to settle a bit, and as they cool the steam migrating through their softening crust can make them a bit tough and leathery. Rewarmed popovers are inevitably hard and dry, a far cry from their just-baked state: crisp shell and soft, rich interior." 

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