Ingredients:

2 teaspoon crushed ginger (or two cubes frozen)
2 cloves of garlic, crushed (or two cubes frozen)
1 Tablespoon neutral oil
1/2 Cup Soy Sause (House Wife Brand recommended)
1/2 Cup Mirin
1/2 Cup Sake
1 Tablespoon Corn Starch
2 Tablespoons Water
2 teaspoons sesame seeds

This is an authentic sauce that can be used for many dishes. It can be kept in the fridge for at least 3 months if jarred while hot and kept refrigerated. To make, take the ginger, garlic and oil and place in a saucepan and sauté for about 3 minutes. Then add the mirin, soy sauce, and Sake and bring to the boil. Once reduced by 1/3 turn off the heat and take the corn starch and water and mix together and add to the saucepan. Sir continuously until thickened. Add the sesame seeds and cook for 1/2 minute further. Pour into a jar and keep until needed.

You should end up with about 1 cup of sauce. You can increase the proportions to make a larger batch and follow the same method.