Line base of a steamer tray with a piece of muslin cloth and arrange the screwpine leaves on the cloth. Spread glutinous rice over the screwpine leaves. Steam for 30-35 minutes.
Meanwhile, combine palm sugar, castor sugar, water and knotted screwpine leaf in a saucepan over a gentle low heat to dissolve. Then strain the palm sugar syrup.
Remove the rice and mix with the coconut milk, salt and syrup in a non-stick wok. Cook over low heat, stirring constantly until the mixture becomes rich and oily. Spread the wajek on a metal tray lined with foil. Flatten out with a piece of plastic sheet and leave aside to cool and harden before cutting into serving pieces.