1.Place split peas in medium bowl; cover with water. Stand 45 minutes; drain. Place peas in medium saucepan, cover with cold water; bring to the boil. Simmer, uncovered, about 10 minutes or until just tender. Drain.
2.Boil, steam or microwave potatoes until tender; drain. Mash until smooth; cool.
3.Combine mashed potatoes, besan, herbs, spices, chilli, egg yolk, juice and salt in large bowl; stir in peas. Mould 2 tablespoons of the mixture into balls then flatten to form patties. Dust patties with remaining besan, shake away excess.
4.For tamarind sauce, combine water and tamarind in small bowl; stand for 30 minutes. Strain tamarind into small pan, pressing pulp to extract all liquid; discard tamarind pulp. Add ginger, cumin and sugar to pan; bring to the boil. Simmer, uncovered, about 5 minutes or until sauce thickens slightly. Strain sauce, serve warm.
5.Heat ghee in large frying pan; dip patties, one at a time in egg. Cook until browned, drain on absorbent paper. Serve patties with tamarind sauce.