Use Jaggery and black sesame seeds in equal proportions, in case you want to scale the recipe up or down.
If the sesame seeds are old, they may not crackle. Jaggery is available in most Indian grocery stores or world markets.
Sucanat can be used as a good alternative. I wouldn't use any kind of sugar though.
Ellu Unde is best consumed within a week of preparation or it can begin to taste rancid.