Have you seen tofu like this before? Freezing tofu gives it a great, spongy texture that makes it really excellent for soaking up soup flavors. The tofu above has been frozen, defrosted, and drained. All you have to do is stick your tofu in the freezer (it'll expand when frozen), and then put it in your refrigerator to defrost a day or two in advance of when you want to use it. Try it some time!
I really appreciate a good, simple salmon miso soup, which is what I used my dong dou fu in. Fish is tricky, as always, as it's easy to overcook. Gentle heat makes it so you won't overshoot as easily. I cooked the salmon at just below a boil until it just cooked through (about 4-5 minutes).
Incidentally, you don't want to boil miso, either, as that will destroy some of its flavor; generally you add miso last. I didn't want over cooked fish either, though, so I did both at the same time. Dong dou fu will be fine--I added it earlier on.
On another note, turnips are a decent substitute for daikon! Daikon's got a bit of a stronger flavor raw, but the turnip seemed to work well in my soup anyway.
Mmm... woops, forgot the wakame seaweed. Oh well, added it for the leftovers.