The classic recipe is made with glutinous rice, but any other type of rice will do. Soak the rice with 2 cups of water (500 ml) for 30 minutes.
In Thailand they steam the rice, but as we haven't a steamer, we add the rice with the water to a saucepan, bring it to a boil and cook over low heat (partially covered) until the water is absorbed and the rice is cooked (about 10-15 minutes, but cooking time may vary depending on the type of rice you're using). Add more water if needed.
While the rice is cooking, make the sauce. Add the coconut milk, sugar and salt in a saucepan and cook over medium-high heat until the mixture is hot and the sugar is melted. Then add the cornstarch dissolved in water, stir and cook until it thickens. Add more or less cornstarch depending on how thick you want your sauce (we usually add 1 and ½ to 2 tsp).
When the rice is ready, transfer it to a mixing bowl and add half of the sauce. Stir until well combined.
Thai people add some toasted mung beans on top. We buy it raw and then toast them in a frying pan, but any other seeds are okay (sesame seeds work great).
To serve the mango sticky rice, add the rice mixture first, then the peeled and chopped mango on the side (½ to 1 mango per serving), some sauce and finally top with the seeds.
Best when fresh, feel free to keep the rice mixture and the sauce (separately) in sealed containers in the fridge for 3 to 4 days. If the sauce is too thick, add some milk or water. Add the mango just before serving.