Here's a mystery I'd love someone to help me solve: Why do people like those awful baby spinach leaves so much? You know the ones—they come pre-picked and prewashed, often in plastic clamshells, nearly flavorless and limp. They've also almost entirely supplanted bunches of full-grown spinach in most produce markets. People actually eat that baby stuff in salads and think it's good. How can that be?
What's most unfortunate is that the now-frequently-MIA adult spinach, especially the curly kind, is truly delicious. Granted, it usually comes with a beach's worth of sand still clinging to it, which makes it a pain to wash properly (maybe this is why the prewashed baby stuff took over?). Point is, we need real spinach back in our lives. Especially for something like ohitashi, the Japanese side dish of blanched greens in a light dashi marinade. Those baby spinach leaves end up squishy and slimy if you so much as blow some hot air in their direction, let alone blanch and marinate them.
When made with spinach, which should be full-grown, ohitashi is called horenso no ohitashi, horenso being the word for spinach and ohitashi referring to the marinating technique that underlies the dish. Spinach is the version I've seen most often in Japanese restaurants in the United States, and it's very common in Japan, too, but it's not the only option for ohitashi. A lot of different leafy greens can work: beet or turnip greens, Swiss chard, dandelion, bok choy, or even the wild watercress I'm using in the photos here. You can even stretch beyond leafy greens to stalk-y vegetables, like asparagus and green beans. Having so many options is a good thing, considering the unfortunate state of spinach in the US today.
No matter what you use, the method is the same—blanch the vegetables until tender, make the marinade, then let them sit together for a while before serving. It's a great vegetable side to have in your arsenal because it's easy and light and can be made ahead, and it's strikingly delicious, with a savory, gently smoky flavor.
So, the first step: Blanch those vegetables. Just get a pot of salted water boiling, drop them in, and cook them for a minute or two until they're tender. Then transfer them to an ice bath right away—in my testing on blanching, the single step that had the biggest effect on preserving a vegetable's bright green color and fresh flavor was stopping the cooking instantly in a bowl of ice water.
Meanwhile, for the marinade, I bring some mirin to a simmer, which helps cook off just a bit of its alcohol, then add usukuchi (light) soy sauce, which is lighter in color but saltier in flavor than dark soy sauce. I combine that with a larger quantity of dashi to form a flavorful broth.
For the dashi, homemade is best, but you can substitute instant if you're in a rush.
Then I squeeze out the excess water from the greens and combine them with the fully cooled marinade, leaving them together in the fridge for at least 30 minutes and up to several hours.
When it's time to serve them, just put the vegetables on a plate, pour some of the marinade on top, and garnish with bonito flakes or sesame seeds. Traditionally, the greens are either arranged neatly lined up in a strip or formed into compressed cylinders, but I kind of like a loosely packed, freeform pile. Whatever the presentation, just...don't use baby spinach.