Boil milk 500 ml,let it simmer, add 1/4 cup of sugar( more if you prefer more sweet) stir well and let the sugar dissolve and let it simmer. Mix 1 tbsp of custard powder in 1/4 cup of cold milk or you can substitute with 1 tbsp of corn starch with 2-3 drops of good vanilla. Add this to hot milk while stirring to prevent lumps. Milk would start getting thicker. Stop once you get the desired consistency.
let it cool. Make mango puree with 2 ripe mangoes. Cube one mango. Once the custard is cool, add the puree and mango chunks. Set it in fridge and serve cool.
This also holds good for all type of fruits. Mix the fruits only after the custard is cold otherwise there are high chances of milk curdling.