Put the rice in a saucepan and add enough water to just cover it. Bring to a boil and cook 3 minutes until beginning to soften, then drain well. Put the rice in a steamer lined with muslin or cheesecloth and steam 12–15 minutes until tender.

Carefully lift the muslin out of the steamer and transfer the rice to a heavy-bottomed saucepan. Add the coconut milk, nutmeg, and 2 tablespoons of the granulated sugar and stir until combined. Bring to a boil, then reduce the heat to low and simmer 6 minutes until thick and creamy, stirring regularly to prevent the rice from sticking to the bottom of the pan.

Line a small baking dish, about 7 x 10in., with plastic wrap, leaving enough overhanging the sides to cover the top when folded over. Spread the rice out to about ¾in. thick and smooth the top with a wet palette knife. Fold the overhanging plastic wrap over the top to cover and then let cool completely.

Peel the mango and slice thinly, discarding the pit. Cut the slices into 16 pieces, each about 1½ x ¾in. Put the remaining granulated sugar and ½ cup water in a small saucepan and stir over a low heat until the sugar dissolves. Turn the heat up to medium-high and boil 2 minutes until reduced and syrupy. Remove from the heat, add the ginger and mango slices, and let cool.

Lift the rice out of the baking dish and remove the plastic wrap. Using a wet knife, cut the rice into 16 pieces, each about 1½ x ¾in. Arrange 1 piece of the mango on top of each rectangle of rice and arrange on a plate. Drizzle with the ginger syrup and serve.