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 3035 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.