While you can do this, cut and slice your potatoes for up to 24 hours in advance and keep the potatoes soaking in cold water in the refrigerator in a large bowl, it is best not to as you will lose a lot of the starch from the potatoes which make the sauce extra creamy. If you do presoak, remove potatoes from water with a slotted spoon or drain well and dry off with a paper towel to keep the potato dish from being watery.