Heat a cast iron griddle (tawa) on medium-high heat. You can also use a non-stick dosa tawa, but cast iron is best for crispy dosa's.
Make sure the tawa is heated well before making dosa. You can sprinkle some water to and it should sizzle right away.
Put a few drops of oil on the tawa and spread with a paper towel all over the tawa. You can also use an onion cut in half and use the flat side to spread the oil. This helps to cool down the tawa and spread the batter in a thin layer. Lower the heat a little while spreading the batter, and change back to medium-high right after spreading the batter.
Take a ladle full of the batter and pour at the center of the tawa. Immediately start to spread the batter from the center out in a circular motion in one direction (I prefer clockwise). Try to spread as thin as possible.
Drizzle oil or ghee around the egdes of the dosa and also some at the center. Let it cook until the dosa becomes golden brown and starts to leave or come out from the edges.
You typically only need to cook one side of the dosa. If you have spread the dosa thick, then you might want to flip it and cook on the other side.
Use a flat spatula to remove the dosa from the edges. You can roll the dosa or fold at the center with the spatula. Remove from the pan and serve immediately.
Before making next dosa, wipe the tawa with a paper towel. Spread the oil again, then spread the dosa. Then increase heat to high.
Serve dosa with sambar, chutney and potato masala.