Based on the story of Satyavan and Savitri each region in India observes a fast in different time of the year. For tamilians, it is called Karadayan Nonbu or Viratham and is observed during the transition of the month Maasi into Phanguni. 

Let me tell you the story briefly. Savitri was the beautiful and intelligent daughter of king Ashtapathi. She had the permission to choose her husband. One day she saw Satyavan in the forest carrying his blind parents in two baskets balanced on either side of a stick. Impressed by his devotion to his parents, Savitri decided to marry Satyavan. Satyavan was under the curse that he would die within the next one year. Even after knowing this, she was adamant and got married to him. 
One year passed happily and then she realised that the time had come for him to die. She started following him wherever he went and she kept this fast. She cooked a special offering to God (adai) and served the same to her family.
One day, while cutting woods Satyavan fainted and she knew that his time had come. She could sense Yama, the God of death around and she followed him as he carried her husband's soul. 
Yama ignored initially thinking that she would return soon. But she persisted
 through all his tricks. Then Yama tried convincing her that it is against the law of nature to return  the life of a dead person and that he can give her three boons instead. 
Savitri agreed and asked for three boons: a son for her father, kindom and glory for her in-laws and then children for herself. 
Thus, she was successful in winning the life of her husband. 

So to this day, married women perform this viratham for the long healthy life of their husband and unmarried girls perform this in order to obtain a good partner.

Karadai with a dollop of butter is offered to God and the below mantra is chanted:

Urugda Venaiyum oru adayum nan veithen.
Oru kaalam yen kanavan yennai piriyatha iruka vendum
(I offer adai and butter to you. So that my husband and I never separate)

Vella Karadai (sweet) 

Rice flour: 1 cup
Jaggery: 1/2 cup
Kaaramani (blackeyed peas): 2 tblspns
Water: 2 cups
Grated coconut: 1/4 cup
Cardamom: 2
Dry roast the rice flour on a kadai (roast till golden brown or till you are able to put a like on medai with a pinch of flour). Cook the kaaramani (do not over cook: pressure cook till 2 whistles) and keep aside.
Soak the jaggery and drain.  Heat the water and add the jaggery. When dissolved, add the karamani and coconut. Mix well. Add the roasted flour at once and mix well without lumps. 
Allow to cool for a few minutes.
Make small thin patties out of the mixture and steam it (i use idly stand for this).
You can be sure that it is done properly if the adai has a shining texture and doesnt have broken edges. 

Uppu Karadai (savoury):
Riceflour: 1 cup
Kaaramani (blackeyed peas): 2 tblspns
Chopped green chillies: 2-3 nos.
Grated coconut: 1/4 cup
Corriander chopped: a few strands
Urad dal: 1 tsp
Mustard seeds: 1 tsp
Asafoetida: a pinch
Water: 2 cups
Salt as per taste
Roast the flour and cook the kaaramani. Keep aside.
Temper the mustard seeds, green chillies, urad dal and asafoetida. Add water and bring to a boil. Add kaaramani, coconut, corriander and salt to this. 
Next, add the roasted flour in one shot and mix well. 
Allow to cool for a few minutes. Make small thin patties and steam.
You can be sure that it is done properly if the adai has a shining texture and doesnt have broken edges. 
Wish you all a long happy life with your partners...
Ciao till next time...Have fun! Vidya.