Cut the broccolini into 5cm (2"). Squeeze as much water out of the broccolini as possible and put them in the bowl with the dressing.
1. You can substitute broccolini with spinach, green beans, Chinese choy sum, Chinese broccoli, or even cabbage.
2. Please refer to Home Style Japanese Dashi Stock for how to make dashi stock. If you are a vegetarian, please use konbu dashi stock.
3. Karashi is different from the Western style mustard and it does not contain acidity nor spices. It is quite hot but the kick from the spice does not last at all unlike chillies. You can buy a tube of karashi mustard at Asina/Japanese grocery stores. But if you cannot find it, you can substitute with hot English mustard or hot mustard. American mustard and Dijon mustard are not suited.