1. Soak the dal in water for 2 hours. Drain and grind with salt to a fluffy batter, using just a sprinkling of water.
2. Heat oil for deep frying, till it is moderately hot.
3. Take a piece of plastic sheet and grease it lightly with oil.
4. Place about 3 Tbsp of the vadai mixture on it.
5. Flatten to a disc, about � cm thick.
6. Make a depression in the center with your fore finger.
7. Transfer it carefully into the oil.
8. Shape 3 or 4 more vadas and drop into the oil.
9. Fry on moderate heat till the vadas are cooked and golden brown.
10. Well made medu vadas are soft and spongy with a thin crisp skin.
11. Take 1 cup of curds and beat till smooth. Add 2-21/2 cup of water and salt. Mix well.
12. Grind coconut with chilies and ginger and add. Add the coriander leaves.
13. Heat the oil in a small fry pan. Add mustard seeds. When they splutter, add curry leaves and add to the curd mixture.
14. Add the hot medu vadas to this thin curd mixture. Let it soak for at least 30 minutes.
15. Beat the remaining curds till smooth. Add salt to taste.
16. To serve, top the soaked vadas with the curds and garnish with boondi

Note:

• Boondis are tiny crisp fried beads of chick pea�s batter.
• They can be made at home or bought from super markets or snack stalls.