Classic Pad ThaiChef Prissana "Fern" Tran of The Florence shares her recipe for pad thai. “The combination of soy and dark soy is like a Thai mother sauce,” she says. “The dark soy is thick, salty, and a little sweet. It adds great umami, but you can’t use much of it because it is so rich. You have to cut it with regular soy. This is the basic sauce for Pad Kee Mao. Add some palm sugar and tamarind paste and you have the basic sauce for Pad Thai. There is no substitute for dark soy.”