Komatsuna, Japanese Mustard Spinach
A Japanese mustard spinach, Komatsuna has a fresh, sweet taste and a crunchy texture. It is a leaf vegetable grown commercially in Japan and Taiwan.
It's a very versatile vegetable and can be stir fried, steamed, boiled, eaten raw in salads or pickled. It's popular in soups as it can stay firm after being simmered.
Komatsuna can be eaten raw or cooked. The flavor of komatsuna is somewhere between that of a mild mustard and cabbage combination. The young tender leaves can be mixed with other greens for salads or use more mature leaves in stir fries. The leaves of komatsuna may be eaten at any stage of their growth. It is also popularly pickled with salt.
Komatsuna is a most under-rated vegetable and is better than other oriental brassicas such as mizuna and bok choi in tenderness, mildness, and versatility.
One great way to eat komatsuna in a traditional Japanese way is to make “ohitashi.” Basically, you blanch the komatsuna by dipping the whole thing (uncut) in boiling water for 30 seconds or so, then dip it in cold water to stop the cooking process. Squeeze out the excess water, cut bite-sized and then dress it up: the traditional way would be a mix of soy sauce and dashi (broth) with katsuobushi (bonito flakes), but you can be creative. Even just soy sauce tastes good.
You read a more detailed recipe about making ohitashi here.