Miso soup has always been one of my favorite simple meals. Growing up, we'd have a near-constant supply of instant miso soup in the fridge. That'd be a packet of dashi granules (like the Japanese version of Knorr Chicken Bouillon), along with a little squeeze tube of miso paste. The kits would perhaps include bits of dried wakame seaweed, some dehydrated scallions, and some dehydrated fried tofu. It was a meal simple enough for a kid to make on a Saturday morning without waking his parents.
Those soups are great, but to compare miso soup from a packet to real-deal miso soup made with an actual dashi stock, high quality miso, and fresh ingredients is like comparing instant chicken noodle soup to your Jewish grandmother's. Assuming you have a Jewish grandmother.
Even between restaurants, quality can vary widely. The worst—which are usually found at the all-you-can-eat sushi and teriyaki houses—taste of not much more than hot salty water with miso stirred into it. I'd be surprised if they were using an actual dashi at all. The best, on the other hand, are complex, multi-faceted affairs.
Rich with the briny flavors of ocean kelp, a hint of rich smokiness from dried smoked bonito, with a deep, earthy, almost cheese-like flavor from high quality, well-aged soybean paste. It's like drinking pure liquid umami gold. There's nothing better to finish your meal with (or to finish off a hangover with, for that matter).
Here's how you do it at home, and it all starts with the stock.
Number One Stock!
Dashi is the base of all Japanese cuisine, and it can be as complex to prepare as it is simple in appearance. Made from only three ingredients—water, kombu (giant sea kelp), and katsuobushi (smoked, dried, shaved bonito)—the process of extracting flavor is one of deep reverence amongst Japanese chefs.
The two major types of dashi are ichiban-dashi—or first dashi—and niban-dashi—second dashi. Ichiban dashi is made by steeping fresh dried kombu and bonito flakes in water that is kept at a sub-simmer. The idea is to use a great deal of kombu and bonito, steeped at a relatively low temperature. By doing so, you develop a broth specific flavors that are best extracted at low temperatures, without extracting many of the heavier, stronger flavors. At the same time, by not allowing the liquid to simmer, you get stock that is crystal clear.
It's very much like brewing a cup of tea, and just like tea, it's finished in a matter of minutes. Ichiban dashi is delicate and mild, used primarily for the clear soups (suimono) that form an essential part to a traditional Japanese meal.
This is not the dashi we are looking for. Move along.
Niban dashi is made by taking the spent bonito flakes and kombu from the first dashi, covering it with more water, them simmering it for a longer period of time—ten minutes or so is normal—to extract what's left of the flavor. What results is a much more intense, slightly cloudy, smoky, briny broth. This is the broth used to make miso soup.
From an ounce of kombu and an ounce of dried bonito flakes, you end up with about a quart of ichiban dashi and a quart of niban dashi.
Now most authentic recipes for miso soup I've found call for this second dashi, but my problem with that is this: In a restaurant setting or in a home that cooks a ton of Japanese food, making both ichiban dashi and niban dashi makes sense—both are used to cook with, and it's more economical to extract as much flavor as possible out of your ingredients.
However, most home cooks outside of Japan aren't going to be cooking enough Japanese food to use up a quart of ichiban dashi every time they want to make a quart of niban dashi to make their miso soup with. So why bother?
Instead, I wondered if I could make a niban-dashi-esque broth right from the start using fresh dried kombu and bonito flakes. Indeed you can. By not bothering with the initial sub-simmer extraction and going straight for a fully simmered niban dashi, you not only extract enough flavor to produce a miso soup as rich as you'd like, but you can also get away with using less kombu and dried bonito.
Tasted side-by-side against a true niban dashi, there are indeed a few differences in flavor and appearance (not to say that one taste better than the other, per se), but once you add the miso, those minor nuances are rendered irrelevant.
As for the miso itself, you can use whatever shade of fermented soybean paste you'd like. White miso, red miso, and dark miso are all used in various regions of Japan. I grew up eating miso soup made with red miso, so that's generally what I go for.
You want to ensure that the miso is entirely lump-free as it gets incorporated into the broth. There are a couple ways to do this. Some folks start with miso in the pot and slowly add hot broth in a steady stream, stirring vigorously with chopsticks or a whisk as the water gets incorporated.
I find it easier to use a fine mesh strainer.
By dipping the strainer down into a pot of hot broth then adding the miso the the top, you can slowly press it through the strainer with the back of a spoon, incorporating it easily. This also conveniently removes any large-ish lumps which you can discard.
As for other ingredients, it's up to you. I personally love the texture and flavor of wakame, a dried seaweed. You can reconstitute it separately in hot water, but personally, I don't have the patience—I just add it to my hot soup and let it soften on its own. Firm silken tofu cubes are a must for me—I love their slippery texture as they heat up in the broth—as are scallions.
If I'm feeling like a miso soup lush, I'll go ahead and add some hon shimeji or slippery nameko mushrooms to the mix, or if I can get my hands on them, tiny cockles.