Soak a piece of kombu (5x5cm) for 30 minutes in the water.
Meanwhile take off the hat and bottom of each mushroom. Set them aside (I use them the following day for a ramen recipe!). Chop each foot into 3 or 4 scallop-size pieces and criss-cross with a knife. Set aside.
Bring the kombu water to a boil. When bubbles start appearing, simmer for 15 minutes, then take out the seaweed, and add nuoc mam sauce. Marinate the « scallops » in this liquid for 20 minutes.
Melt the butter in a pan. Meanwhile coat the “scallops” with corn starch. Flash-fry for 2 minutes maximum on each side, until golden and crispy.
NB. Here served with wholewheat spaghetti, fresh agretti, my cream of lemon sauce (see recipe), asparagus with pistachio oil and chopped wild garlic.