Larger tongues can take much longer to cook, so choose the smallest tongue you can find, ideally below 3 pounds / 1.4 kg. Tongue has a short shelf life, so purchase it very fresh or frozen from a reliable butcher. (If frozen, thaw in the refrigerator for maximum safety.)  Some tongues include the glands, bones, and fat at the root of the tongue. This area is edible when cooked, but not everyone likes the soft, fatty texture. You may cut it off at home (before or after cooking), or look for a pre-trimmed "Swiss cut" tongue.  Brined tongue packs extra flavor and can be prepared the same way as fresh tongue. Place the tongue in a clean sink and scrub thoroughly under cold running water. Clean until the surface is free of dirt and blood. Many recipes recommend soaking the tongue in cold water for an hour or two, changing the water whenever it becomes murky. Store-bought tongue is usually clean enough to skip this step, but it can freshen up the tongue's flavor. Fill a large pot with chick or beef stock, or moderately salted water. Add vegetables and herbs of your choice. An onion or two, a couple bay leaves, peppercorns, and a carrot form a good simple base. Feel free to add other ingredients, such as oregano, rosemary, garlic, or chiles. Bring to a boil over high heat.  Use a pressure cooker or slow cooker to speed up the process. If you want to create a thicker sauce to serve with the tongue, add four cans of condensed French onion soup. Add the tongue to the broth and cover the pot. Bring to a boil again, then reduce to a simmer. Keep the tongue completely submerged. You may need to add more water or weigh it down with a steamer basket. The tongue is ready when it turns white and a knife easily pierces the thickest part. This typically takes about 50–60 minutes per pound (0.45 kg) of meat.  Fast cooking or undercooking makes the tongue tough and unpleasant. If you've got the time, err on the side of caution and keep simmering for an extra hour or two. If using a pressure cooker, heat until it starts to steam....

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Write a summary of the previous text in Vietnamese:
Mua lưỡi bò. Làm sạch lưỡi bò. Chuẩn bị nước dùng. Cho lưỡi vào nồi. Đun liu riu đến khi lưỡi bò mềm. Lột lưỡi bò khi còn ấm. Cắt thịt thành lát 0,5 cm. Bảo quản phần thịt còn thừa trong tủ lạnh.