Hat doi is a rare Vietnamese spice, also known as Northwest Black Gold. It is often used in combination with mat khen pepper, chili pepper, and salt to marinate meats. It is also used to season grilled fish, make sauces for dipping meat or fish, and to flavor duck blood soup (tiết canh vịt).

Its intense and unique aroma is unmistakable, typical of dishes from northwest Vietnam. Traditionally, the seeds are roasted over embers before being finely ground, but you can also dry-roast them in a pan and then grind them in a mill or mortar.

Hat doi comes from the seeds of a specific species of magnolia native to the mountainous forests of northwest Vietnam. Red when fresh, it turns almost black after being dried in the sun, hence its nickname "black gold."