Need some au gratin potato advice
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!
Slice and cook the potatoes first. Boil or zap in the microwave. Make a beschamel sauce, fairly thin. Add shredded cheese of choice. Add spices or herbs of choice (sauteed onions, garlic, persley, chives, etc). Drain potatoes, mix with the sauce and bake until slightly brown on top. Refrigerate for a day or so, and rebake to serve. They are better a day or so later. Trust me. The problen with the traditional method, is the tendency of the cheese to separate in the baking. I always melt the cheese in a beschamel to prevent that.
Potatoes au gratin are always better made a day or two or three ahead, in my opinion. I never parboil or do any kind of precooking the potatoes. Mine cook for 90 minutes, so I time the initial bake for 75 minutes, or until they are just starting to brown. When they are cool enough, refigerate them. If they are still warm, put a couple of layers of paper towels over them before putting on the plastic wrap. This way you won't get condensation all over your potatoes. Let them bake for another 30 minutes at the party locale.
You can make the whole thing ahead and reheat it at your friend's house. Just make the sauce a slight bit thinner than usual, and don't overheat when reheating or cooking or the sauce might separate. Also, brown the top the first time around.
I would not preslice the potatoes or try to keep them raw to cook later. They'll probably turn color and that wouldn't save much time anyway.