This recipe calls for both regular and dark soy sauces. Dark soy sauce is sweeter and thicker than regular soy sauce. It's also used as a food coloring to impart deep caramel hues to meat, noodles and stir fries. Read all about dark soy sauce here. However, it's not an obligatory ingredient for this recipe. You can either skip it and just use regular soy sauce in its place - or pick some up here on Amazon.