½ cup soy sauce
½ cup mirin
¼ cup sake
½ cup brown sugar
4 garlic cloves, roughly chopped
3 spring onions (scallions), root end trimmed
4cm piece ginger, sliced
Place the ingredients in a saucepan over medium-high heat. Bring to a boil, then reduce heat to medium and simmer until the sauce has reduced by half. Then strain and set aside until ready to serve.