An Appachatti Pan is a stove-top frying pan that’s completely rounded at the sides, so that it’s like a shallow bowl. It has two short handles, one on each side, and will come with a cover usually.
They can be can be cast-iron or non-stick metal. Cast iron ones are getting hard to find, but people swear by them.
They are used for making “vella appam” in (“kuzhi appam” pans are different; see Appakarai Pans.)
To use, you first heat the pan well, then pour a large spoonful of appam batter in. You lift the pan using both handles, and swirl the batter inside so that it coats the entire bottom. Cover and cook for about 2 minutes.
At the edges of the appam, you’ll end up with a lace-like pattern.
If using cast iron, heat a small amount of oil in it first before starting.