Remove the stems from the komatsuna and slice into 3-4 cm lengths. Slice the pork into easy to eat lengths, and cut the atsuage into bite-sized pieces.
Put the dashi stock, soy sauce, mirin, sugar and atsuage in a sauce pan and turn on the heat. When it has come to the boil, add the pork and komatsuna and turn the heat to medium. Simmer for 5-6 minutes, loosening up the pork occasionally.
Add the Japanese mustard (optional) and it's done once it has come to the boil. The colour won't be so nice, but it's even tastier if you let it cool down, then heat it again before eating.
Story Behind this Recipe
I love green leafy veggies like komatsuna with atsuage (or aburaage), so I make this often. I thought that if I added meat, it would make a hearty side dish.