to make the teriyaki sauce

1. Whisk the brown sugar, mirin, sake and soy sauce in a bowl. Set aside.
2. Warm the toasted sesame oil in a small saucepan over medium heat. Add in the ginger, making sure it’s coated well with the oil. Saute for 1 minute only.
3. Pour the contents of the bowl into the saucepan, whisking it initially to dissolve the sugar. Once it comes to a small boil, reduce the heat to its lowest setting. Allow to reduce for 30-35 minutes, whisking it occasionally, then remove from the heat.
4. Chill the teriyaki sauce to allow it to thicken before using. If it becomes too thick (it will be thicker if you did not use sake), a few seconds in the microwave will loosen it up enough to pour.

to prepare the king oyster mushrooms

1. Slice them lengthwise, then score them by slicing diagonal lines down the length, then crosshatching them in the opposite direction.
2. Combine the broth, sesame oil and hoisin in a large pyrex. Place the sliced and scored mushrooms face down and allow to marinate for about 20 minutes. Pick the mushrooms up and rub the marinade all over.
3. Heat a large cast iron skillet over medium-high heat. Add a little oil to the pan, then add 2-4 pieces of mushroom in the pan, face down. Be careful, the mushrooms may sputter a bit when they hit the pan, so use caution. Check them after a minute or two. Once they have a nice, deep color, flip and allow to sear on the other side.
4. Transfer to serving plates and drizzle with the desired amount of teriyaki sauce. These mushrooms are great served with a side of bok choy and rice!