I was planning on making au gratin potatoes for this bday dinner party for my friend. She just moved it to Friday from Saturday and still wants them but I don't have time to prepare and bake when I get home from work and still make it to the party on time. The recipe I have uses raw potatoes and a cheese/milk sauce poured over then baked for 1.25 hours. Can I slice the potatoes and pour the sauce over the night before without baking till Friday? Will the potatoes soak up all the liquid? Will they turn grey? Also, could I slice the potatoes and put in a ziplock the night before then bake with sauce the next day? I'm not an au gratin or potato starch expert. Help!