Some people mash potatoes and freeze. I have never done this as i don't think they would turn out well. I think they become watery so if you do this just stir, stir, stir when reheating.
This is my family's favorite scalloped potato recipe:
1/2 c. chopped onion 2 Tbs. butter 3 Tbs. flour S&P
1 1/2 c milk 2 tsp. seasonings ( basil, oregano, thyme,whatever you like) 4-5 medium potatoes, thinly sliced
Sauce: cook onion in butter until tender Stir in flour, S&P.....cook for 1 minute. Slowly stir in milk and cook until thickened. Stir in additional seasonings.
Place potatoes in bottom of sprayed baking dish. Pour sauce over top. Bake, covered, at 350 for 45 min. to 1 hour-until potatoes are done.
You can also sprinkle shredded cheese on top. I usually add ham and corn to it and make it a one-pot meal.
*Note* if you have 1/2-1 c. broth, use that in place of some of the milk for added flavor.