The typical Vietnamese family meal consists of several communal dishes: one or two protein dishes (my family normally does 2: one lighter steamed or poached dish and one braised or sautéed dish with stronger flavors), a boiled or sautéed vegetable dish, and a bowl of canh.
The canh is a soup. Most of our canh options are leafy green-based, but there are some exceptions like this beautiful purple yam soup.
Commonly known in the U.S. as “Ube” – not to be confused with purple sweet potato, this purple yam is called “khoai mỡ” in Vietnamese. Khoai refers to potato and most tubers and mỡ means “fat” – this may be because if you cut a cross section of the yam, it has a dotted pattern that looks like bits of minced fat or because of its creamy texture when cooked. I grew up calling it “khoai tím”, which just means purple tuber. And purple it certainly is- such a striking color whose vibrance surprises me every time I cook it.
You can either use whole or frozen grated yam. Important note: the raw skin of the yam has a skin irritant (which doesn’t cause issues once cooked). So if you have sensitive skin, I would recommend wearing gloves while handling it or using the frozen kind.
While the yam is the star of the show, this soup cannot be complete without ngò gai and/or ngò om (culantro and rice paddy herb, respectively). If you absolutely cannot find them in your local Asian grocery store, add extra green onions.