Slice bitter gourd, raw banana, and potato into long batons.
Grind mustard seeds with a little water into a paste.
Heat ghee in a pot, shallow-fry bitter gourd slices lightly; remove.
In same ghee, temper panch phoron, add ginger paste, potatoes, raw banana, water, and salt; boil until tender.
Stir in mustard paste, fried bitter gourd, and milk; simmer gently for 5 minutes and serve warm.