To prepare sauce, remove stems and boil whole red chillies in one cup of water for five to seven minutes. When cool grind the red chillies to a fine paste. Heat oil, add chopped garlic, green chillies, spring onions and grated ginger and sauté for a minute. Add the red chilli paste and continue to sauté. Add vegetable stock or water, celery, tomato ketchup, salt and stir to blend well. Add vinegar and chopped spring onion greens. Simmer for a minute and take off the heat. Cool and store.
Wash rice two to three times, clean and soak in fresh water for at least 2-3 hours. Wash and soak the dal also for a similar time. Add the methi seeds to the soaking dal. Drain and grind the rice to a slightly coarse texture and dropping consistency. Drain and grind the dal, sprinkling water as required to a smooth and spongy batter. Mix both the batters with salt with hand, thoroughly in a whipping motion. Keep the batter in a large vessel, close tightly and rest the batter in a warm place for at least 24 hours.
Mix the batter well and pour into lightly oiled idli trays and steam for about 10 to 15 minutes. Dip a toothpick into the idli to check if done. Remove idli from moulds, and allow to cool completely. Cut idlies into one-inch batons and deep fry in sufficient hot oil till golden crisp. Drain onto an absorbent paper and serve hot with Sichuan sauce.