The next time you make mashed potatoes, fix extra and use them to make duchess potatoes.
Add 1 beaten egg to every 2 cups of mashed potatoes, then pipe or mound onto a parchment-lined baking sheet. Freeze until firm, then transfer to a plastic bag, and keep frozen up to 3 months.
To use, place frozen potatoes onto a greased baking sheet and drizzle with melted butter. Bake at 375° for 25 minutes, or until heated all the way through with edges turning crispy and brown. This also works with mashed sweet potatoes