Soak rice in a generous amount of water overnight. Strain. Line base of a large bamboo steamer with a circle of baking paper. The paper should come about 2cm up the sides of the steamer. Prick the paper all over with a fork (this will allow for the steam to permeate). Place rice in the steamer and spread evenly over the base.
Partially fill a large wok with water – ensuring that the base of the steamer will not touch the water. Bring to the boil. Place lid on steamer and place into wok. Steam for 10 minutes. Remove lid and sprinkle rice with 2 tablespoons of boiling water, then stir rice gently with a large metal spoon. Replace lid and continue steaming rice for 10 minutes longer or until cooked. The rice grains are cooked when they are translucent and soft but slightly chewy. Spoon rice into a large heatproof bowl.
Meanwhile, prepare kaffir lime syrup. Place palm sugar and 2/3 cup of water into a small saucepan. Stir to dissolve over low heat; increase heat and boil for 8 minutes, without stirring, until thickened slightly. Remove from heat and stir in lime zest and kaffir lime leaves. Stand 10 minutes, then strain through a fine sieve, pushing down on any solids to extract flavour.
Pour the coconut milk into a medium saucepan. Add sugar and salt. Stir over medium heat until the sugar is dissolved, then bring just to boiling point. As soon as rice is out of the steamer, pour hot mixture over rice and stir to combine. Allow to stand for 5 minutes.
Meanwhile, lightly brush a grill pan with canola oil. Place over medium heat; grill mango cheeks for 1-2 minutes each side or until charred. Serve grilled mango with the rice; drizzle over the kaffir lime syrup and top with finely sliced kaffir lime leaves. Serve immediately.
