This is a Bengali sweet enthusiastically devoured by our family, if we can't buy it from the halwai, or buy it in tins, I sometimes make this at home.
This can be used either as rusgullas, or as the filler for rasmalai.
Why do I call it rusgullas - because I grew up in the hindi heartland of India, Uttar Pradesh where they are called"rusgullas". The UP halwais give the Bengali halwais a run for their money - however before plunging into a regional war..here is my recipe..which is probably not the original, but which works for me...and has been devoured happily in our home.

You need:
1.5 cups of full fat milk powder ( I use Sunshine in Australia, or Glaxo in India)
1 egg
1.5 cups fine white sugar
3 cups of filtered water
a few crystals of sugar (called misri in hindi)
a few drops of rose essence (essence not rose water)

Steps

1. Beat the egg and use it to knead the milk powder into a soft dough with minimal handling
2. Add the sugar to the water. Place it on a slow fire and make a thin syrup. Do not allow it to boil.
3. Make small balls from the dough, placing a single misri in the centre of each, and sealing the ball firmly.
4. Place all the balls into the gently simmering syrup.
5. Cover the pan with a tight lid and cook gently for 15 minutes, or until the balls have doubled in size.
6. Remove the pan from the heat, and allow to cool.
7. When cool, add the rose essence and shake the pan about gently.