You can soak and grind everything together too. But make sure it is ground really smooth.
(OR) Soak both rice, dal in one vessel along with poha and urad dal, fenugreek seeds in another vessel for 3 hrs.
First grind fenugreek till smooth and fluffy adding around ½ cup water, then add rest of the soaked items, enough water and grind till smooth.
Mix salt and keep for fermentation overnight. Batter should be little bit watery than idly batter (just pouring consistency) and should not be heavy, should be light.
So take required amount of batter, add water or coconut milk for authentic taste to dilute it.
Before you decide to make aapam, add the cooking soda and stir well.
Heat a heavy bottomed kadai and pour 1 & ½ ladle of batter.
Just spread in the sides of the pan like we spread dosa, leaving little batter still in the middle ( I find this method easier and quicker). This will give you thin edges, just like if we rotate the pan.
If you are convenient in rotating the pan, then hold the two sides of the pan and rotate in a circular motion to get a thin edge.
If you use oil just drizzle a few drops after you make the appam, because if you add oil before, then batter will not spread evenly.
Cook covered in a medium low flame. After a minute check for doneness. Once you do not see whitish spot, or raw batter in middle, you can take it out.