Peel the yam and cut into cubes. Boil the pieces in enough water to cover an inch above the pieces with turmeric and salt.
Drain the water when the pieces are cooked and cool the yam.
Grind a tablespoon of grated coconut with a handful of peeled sambar onions and 1 tsp of sombu (aniseeds, fennel)
Heat a tbsp of oil in a thick bottomed pan and put in a tsp of mustard seeds.
When they pop add a sprig of curry leaves and the ground paste.
Saute for a few minutes with a tsp of salt, 1 tsp of chilli powder and 1 tsp of coriander powder.
Add the yam pieces and continue sauteing on medium heat.
Let the yam brown over low heat without burning the masala.