Add baking powder to the mixture, if needed, as it will cause them to puff up and lighten when cooked. Adding a little cream may also help.
I have a Gulab Jamun recipe from "Dance of Spices" by Laxmi Hiremath, pg 412, which lists the following for the dough:
- 0.5 cup (120 mL) unbleached all-purpose flour
- 2 cups (around 470 mL) powdered nonfat dry milk
- 1 tsp (5 mL) baking powder
- 1 cup (236 mL) heavy whipping cream (probably listed as "double cream" where you live, see question on cream types)
- about 1 TBSP water (15 mL)
The dry ingredients are mixed, then the cream is gradually mixed in, and the water is added to make a smooth, pliable dough.