When you go to a Vietnamese restaurant in Vietnam or abroad, there is often super thin shreds of cabbage and or banana blossom that are presented as garnishes for dishes such as bun bo Hue spicy beef and pork noodle soup. Cabbage salad with chicken and Vietnamese coriander is a classic dish in which shredded cabbage is featured. So how do those clever Vietnamese cooks get those thin shreds?
Several people have asked. For example, Diana in New Zealand inquired a while back, saying that her mother in-law claims that only a special knife from Hanoi yields those unmistakable thin slices. John, who read the post on finely shredding ingredients, asked if a mandoline works well, and how it compares to a knife.
What Diana's m.i.l. was referring to is a tool called a dao bào ("zow bow"). It's a Southeast Asian vegetable knife/peeler/slicer that resembles a knife but has a peeler type of blade cut into the main blade, which is also very sharp. I've often seen it used to shave off very thin slices of banana blossom and cabbage. In the States, you'd buy it from a Vietnamese grocery store. The photo below shows the two main versions, the modern (and safer) one with a plastic handle is on top and the more rustic version with the steel blade is below.
The knifes are often labeled a vegetable peeler but can be used for peeling and slicing. The rustic version can be used to chop too, like a regular knife, though it's not as precise. It can be unscrewed and sharpened easily, though after washing, I found that the blade rusted easily.
I've not seen either kind sold on the Web, and it's likely not to be since the dao bào became somewhat controversial with the shooting of a Vietnamese American woman who was mistakenly killed for wielding a rustic version at a police officer. (Read story)
When trying out both of these dao bào I found that they just weren't as great as using a regular knife. Surely, if you're squatting without a cutting board, holding a wedge of cabbage or banana blossom and using the knifes directly over a bowl into which the shaved pieces would go, is quite handy. But for me, I'm standing at a kitchen counter and there's always a piece of the vegetable leftover that I end up cutting with a knife since I can't use the dao bào on it.
However, I don't see why you need a special knife to thinly slice up cabbage or banana blossom. If you use a sharp Japanese style vegetable knife, which has a thin blade, you'll get nice thin shreds; those knives (called usuba; see sample knife) typically have thin rectangular blades. Your salad or soup garnish won't be ruined if you don't have the knife.
Actually, traditional Viet cooks didn't have that special slicers/shredders/dao bào to use. They employed their multipurpose kitchen knife and kept it sharp. Get your knifes professionally sharpened occasionally and steel it before you use it. Your sharpening professional should teach you how to maintain your knives.
Also, if you have a firm, tight head of fresh cabbage or banana blossom, cutting a thin shred works too. I suppose you could use a mandolin, as well, as John suggested. But unless you have a huge quantity of cabbage or banana blossom to slice, I don't see the need to bring out the mandolin.
Related information: Finely Shredding Ingredients