In a small bowl, combine custard powder with ¼ cup of milk. Whisk well and set aside.
Combine rest of the milk and sugar in a medium size saucepan. Bring to a boil on medium heat.
Once the milk comes to a boil, remove from heat and slowly add the custard powder mixture by whisking continuously. Place the pan back on medium heat. While whisking continuously, bring the mixture to a simmer and cook until the mixture thickens and coats the back of a spoon. This takes about 4-5 minutes.
Remove that custard to a bowl and let it cool down for 5-7 minutes. Then add mango puree and mango pieces. Mix well. Do not add mango puree to the hot custard mixture otherwise, it loses its fresh mango flavor. Always cool the cooked mixture slightly and then add. When it comes to room temperature, chill the mango custard in the refrigerator.