Per Wikipedia (which I will deny using as a source if you tell any of my former writing students), tatsoi is also referred to as spinach mustard, spoon mustard, or rosette bok choy for the shape of the clusters the leaves grow in. For such a crisp and seemingly delicate green, it's apparently very hearty--it can tolerate temperatures as low as 15 F and can be harvested from under the snow! (If so, it seems this might be a good candidate for growing more locally, even through the coldest winter months.) The kitchen dicitionary at RecipeZaar likens the flavor to bok choy, but I would argue it's got a little more bite--it's grassy, lemony, and mustardy all at once, and boy does it jazz up a bowlful of red leaf lettuce! RecipeZaar also suggests tossing it into soups just before serving, which I imagine might work well with Asian flavors.
Though I haven't tried it yet, there was also a delectable-sounding recipe in the e-newsletter. You can find it below, and you can bet that I will be giving it a shot the next time these yummy rosettes come my way. Keep your eye out for them at your nearest winter farmers market--they are a lovely treat!
Chilled Sesame Ginger Tatsoi,
From the Enterprise Farm Newsletter
1 1/2 lbs Tatsoi, washed & dried
salt & pepper to taste
1/3 c soy sauce
2 T sugar
4 dashes Tobasco sauce
1/4 c white vinegar
2 T sesame oil
1 T ginger, minced
1/4 c sesame seeds, toasted
Bring a large pot of salted water to a roiling boil. Add the tatsoi, blanch for 1 minute, drain, and immediately plunge into ice water to stop cooking. Drain again.
In a small bowl, combine the soy sauce, sesame oil, ginger, sugar, vinegar, and Tobasco. Mix well and season to taste with salt and pepper.
In a large bowl, combine the tatsoi and dressing. Mix well and refrigerate until well chilled. Garnish with sesame seeds and serve.