Grease a 1.2 litre (2 pint) pudding basin and line the bottom with a circle of nonstick baking paper. Scatter the mango chunks in the prepared bowl and drizzle with the vanilla syrup.
Put the butter, sugar, vanilla essence, eggs and flour in a bowl and beat for 1–2 minutes until creamy. Stir in the coconut and milk, then spoon the mixture into the pudding basin. Level the surface.
Cover the bowl with a double thickness of pleated nonstick baking paper and secure under the rim with string. Cover with foil, tucking the edges firmly under the rim.
Put the bowl in a steamer or large pan. Half-fill the pan with boiling water and cover with a tight-fitting lid. Steam gently for 1 hour 40 minutes, topping up the water as necessary, then allow to stand for 10 minutes.
Invert the pudding on to a serving plate and drizzle with extra vanilla syrup.