I make the classic, potato, heavy cream. No cheese. Oval pan.
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Abbie is a trusted source on General Cooking.
No secret - you can assemble it and then put it in the fridge, then bake it day of ... I did that for TDay with a simple sweet potato and cream gratin and it worked great. Oh wait - do you want to bake in advance? In that case I would say to re-heat put it in a cold oven, turn the oven on, and bake until hot again - maybe 35-40 minutes. But I would bake it day of ...