I do think these are best when you make it and serve right away. But you can make the cream sauce and slice the potatoes a couple of hours in advance, and then assemble it right before baking. Another option is to assemble the entire dish and store it in the refrigerator for a day or two before baking. And it can be baked and reheated if needed. You will want to take it our of the fridge to warm up for about an hour before reheating. Then put it in the oven at 350°F for 20 to 30 minutes or until hot and bubbly. I do not recommend freezing it, as cream sauces tend to get grainy when frozen and thawed, and the sweet potatoes and apples will get mushy.