Use 5 sheets of stale nori seaweed. You can use fresh crispy nori of course.
Rip the nori sheets up in a bowl. Add about 200 ml of water, and leave it to soak for more than 20 minutes. Stir occasionally.
In the meantime, slice the reconstituted dried shiitake mushrooms. Cut the stems off and slice the caps thinly. Cut the hard end off the stems and slice them up too.
After 25 minutes the nori looks like this. When it has disintegrated completely into a paste, it's good to go.
Drain into a sieve.
Transfer to a pan and add all the flavoring ingredients. Cook over medium heat. When it comes to a boil lower the heat.
Simmer gently until there's no moisture left in the pan for about 20 minutes
Tilt the pan; when there's about 1 tablespoon of liquid left in the pan, turn the heat up to high and mix to evaporate that moisture and dry out the nori a little. Be careful not to let it burn.
When there's almost no moisture left it's done. Store in a jar that's been sterilized in boiling water. Refrigerate when cool.
To make your own dried shiitake mushrooms, see
https://cookpad.com/us/recipes/143982-sun-dried-shiitake-mushrooms-with-butter-and-soy-sauce
