Fermented mustard greens give a specific taste that you find a lot in Chinese or Taiwanese cuisine. We use them in our classic bao with pork. The round, mellow, sour notes work really well to cut through fatty food in a balanced way.

They make a refreshing pickle; if I grill a fish, I’ll have them on the side to eat every other bite. When I make a simple chicken broth, I’ll add fermented mustard greens to season it with a sour taste – perfect for rainy winter weather. I often eat mustard greens in a noodle dishHaving it as a soup noodle has a cleaner taste, but if you want a dry noodle, you’d probably stir-fry it first with soy sauce, and then add your noodles.

They are the secret ingredient in my fried rice. If I have leftover roast duck, I’ll scrape off the fat and use it to fry the mustard greens. The greens are coated in all that flavour, which then goes into the rice, giving you a salty burst with every mouthful. Duck and fermented mustard greens is a classic combo.

We make our own in the restaurants but in Asian grocers you can buy them in large pieces in a vac-pack, or chopped in a jar.  Mustard greens have a distinctive flavour, nice soft leaves, and a stem that is really juicy and crunchy when pickled. We sometimes use pak choi, but this has more water content so once it is fermented, the texture is softer.

If you want to make your own, which I recommend, you can buy mustard greens from Asian grocers, or online – or you can use other greens available to you. I suggest that you wash your veg clean, then weigh it and combine with 2% of the weight in salt. Then really squeeze your veg into a jar and the liquid will naturally come out – you don’t need to add any more. Let it ferment it for at least two weeks. One month will be tastier. I give them a rinse before I use them because they are salty to the core.

Erchen Chang is a chef and co-founder of Bao, London