When cooking tofu in the Vietnamese way, we eat it with a sauce made of fish sauce & spring onions. We never refer to it as that, just as ‘fish sauce’, but since we eat it one or two times a week and we never it with anything else, we never question it.
You use the green part of the spring onion. It’s really important that when you cut the onion you slice green part thinly. the green stalk of the spring onion contains a gooey, slimy gunk that is brought out both by the salt in the fish sauce and the degree to which it is exposed to this. Slice the onion thickly and there is less goo exposed to the fish sauce. Slice it thinly and there is more. It’s crucial to get it as thin as possible. You can approximately the effect by chopping up the result. similarly, don’t overdo the fish sauce. put in a 3rd of a small bowl and then add the onion and mix. Mix up the onion until it is all wet. You should start to see a similar effect to honey and mustard.
Here’s how it looks when done well:
Eat with fresh cooked sticky white rice and boiled vegetables. Perfect!