Wash the lentils, then place in a bowl with fenugreek seeds and allow to soak for four hours.
Wash rice and place in a pan with one litre of cold water. Bring to the boil, then reduce heat to a low simmer. Cook for five minutes or until just parboiled. Remove from heat, drain the water, reserving it for later.
Drain the lentils and fenugreek seeds, reserving the water for later.
Grind or puree the rice to make a smooth batter, adding as little of the reserved rice cooking water as possible.
Grind or puree the urad dal and fenugreek seeds with some of the reserved soaking water until you get a smooth and fluffy batter.
Mix both the batters together in a large bowl with the fruit salt and mix well. Cover and let the batter ferment overnight at a warm room temperature - at least 20C. After the fermentation process is over the batter should be doubled in size with many small air bubbles.
notes
This recipe must be started the day before. You need to soak the lentils for around four hours, then allow the mixture to ferment overnight.
Fruit salt is marketed under the brand name Eno. It is best obtained from a pharmacist, as supermarkets seem to only stock flavoured variants. For this recipe, you can substitute baking powder.