Use your hands to mold your leftover mashed potatoes into .5 in (1.3 cm) thick patties. Place the patties on a baking sheet, then cover it with plastic cling wrap. Put the mashed potatoes into the freezer for about 24 hours. Then, combine the mashed potato patties into a single airtight container. It’s best to eat them within a few weeks, as mashed potatoes don’t freeze well. Cool the dish evenly by putting it in your refrigerator for about 1-2 hours. Cover the food with moisture-resistant parchment paper, then cover it again with a lid or aluminum foil. When you're ready to reheat the dish, you can thaw it or put it directly into the oven while it's still frozen.  These types of potato dishes can be reheated in an oven at 400 °F (204 °C) for 25-30 minutes. If you have one, use a food thermometer to make sure the dish's internal temperature is at least 165 °F (74 °C). If you're making the recipe with the intention of freezing it, stop cooking the dish when it has a light brown color and the potatoes feel almost tender.

How would you rephrase that briefly using Vietnamese?
Đông lạnh khoai tây nghiền được nặn thành miếng dẹt đặt trong khay nướng bánh. Bảo quản món khoai tây nhồi và khoai tây hầm trong đĩa khi đông lạnh.