Almost exactly 5 years ago this week I was on a study tour to Japan to look at Sansai production. I’m doing a webinar talk about the trip for Norwegian Seed Savers (KVANN) on 18th April. Although it’s open for all it will be in Norwegian. If there is interest for it I could repeat in English at some stage, but probably not before next winter. If anyone would like to organise it, please let me know. Otherwise, I may just organise it as the first Edimentals talk!  See https://www.facebook.com/events/1333421547030675
Sansai (meaning mountain vegetables, mostly perennials) are what are essentially previously wild foraged vegetables which are now produced on farms in the lowlands around the cities in Japan, often in greenhouses for all year production – roots are often frozen until they are needed). 
With a little planning one can extend the season for some of the best sansai vegetables by digging up roots in the autumn and planting them in soil in buckets which are stored in my cold cellar (just above 0C this winter), and ready to be brought up into the living room for forcing in winter / spring (they could also be left outside, protected by piling leaves or similar around them – the roots are more exposed to cold in a bucket). For blanching I use a second upturned bucket on top. I’ve now harvested three important sansai veggies which were forced (it took a couple of weeks);
Udo (Aralia cordata): peeled and sliced and eaten as a salad in a sesame oil and soy sauce with roasted sesame seed dressing
Ostrich Fern (Matteuccia struthiopteris): steamed for 10 minutes
Urui (Hosta sieboldiana): The blanched shoots are deliciously crispy and mild tasting, perfect with a dipping sauce (sesame oil, roasted sesame seeds and soy sauce)
The sansai were served with fried veggie beetroot burgers (aka blood burgers) which are cooked and grated beetroot mixed with egg and wholegrain emmer flour (with grated onion, garlic, chili, salt and pepper).