Take 2.5 cups of Idli Batter in a bowl and adjust consistency by adding 1/4 cup of water and salt to taste Note - Add very little salt as idli batter already contains salt.
Finely chop the Onions, green chillies and keep aside.
Heat a griddle or dosa pan, add few drops of oil and with a kitchen paper towel, wipe the surface well.
Now carefully pour a ladle of batter in the centre of the griddle and spread clockwise, ensuring the centre is slightly thick.
Quickly top the batter with chopped onions, some green chillies. Pat the onions with your spatula so that the batter absorbs it well.
Pour some oil on the sides and in the centre and cover the pan with a lid.
Ensure the flame is medium and allow the Uttapam to cook
Once you see the edges have cooked (brown), carefully flip it, pour some more oil and allow it cook.
Once the top has caramelized, remove from pan and Serve it piping hot with chutney of your choice.