Miso Fish Fillet with Mixed Mushrooms

This is absolutely wonderful. This recipe was originally created by Roy Yamaguchi. I tried it using salmon for dinner for my son, Josh and his friends and it was great!
Miso, Mirin and Sake can all be found in any Asian grocery store.  You will find Miso in the refrigerated section.

Ingredients:
4 6oz fillets (salmon or cod)
3/4 cup sugar
1 1/4 cup miso
1/2 cup Sake
1/2 cup mirin (Japanese sweet rice wine)
2 cloves garlic (minced)
2 tblsp unsalted butter
1 lb mixed mushrooms (cleaned and sliced)
2 tsp lemon juice
3 tsp soy sauce
Olive oil
Salt and pepper

In a sauce pan on medium heat, add sugar, miso, sake and mirin and whisk together. Bring the marinade to a slow boil, then remove from heat. Allow marinade to cool.  Place the fish fillets in a shallow dish; pour the marinade over the fish.  Cover and refrigerate for 1 hour or overnight.
In a large skillet heat butter and add the garlic. Saute garlic for approximately 2 minute until lightly brown.  Add the mushrooms and saute until a light golden brown, about 10 minutes. Add lemon juice and soy sauce, continue to saute. Season with salt and pepper. Set aside and keep warm.
Liberally oil grill and heat to medium-high. Grill the fish, turning once, until cooked through, approximately 3 minutes per side. Serve with the mushrooms and rice.