Đổ nước lạnh và khoai tây vào nồi. Đun sôi nước. Tắt bếp sau khi hết thời gian đã đặt ra. Ngâm khoai tây ngay vào nước lạnh.

Given the above summary, write a detailed text in English for it.
You want enough water to reach about 1" (2 cm or so) above your potatoes. This way they'll all cook evenly. Make sure your potatoes are clean and to size! You want to do them all at once, if possible, to make sure they're all the same level of doneness. Boil small to medium potatoes for approximately 7-10 minutes; boil larger potatoes for approximately 12-15 minutes. Some people swear on bringing the potatoes to a boil and immediately turning it off, leaving the potatoes in the hot water on the hot burner. This method generally takes a solid 15 minutes, but is better for ensuring you don't overcook your potatoes. If you're not sure how "done" the potato is, stick a fork into it. Preferably there should be a cooked outer edge and a raw middle; the potato should still be firm and your fork should meet resistance after the initial edge lets it through easily You can also take your knife to the edge of the potato. Do the edges come off all nice and fluffy-like? When you get to the center, is it whiter, harder, and clearly a bit uncooked? That's perfect. This stops the cooking immediately. They are now ready to be used as required in your recipe. Parboiled potatoes will not keep for very long time – aim to use them within a day or two, at most. Keep them in the fridge in a bowl, not a plastic bag (this causes them to sweat, softening them).