You will need a medium-sized mixing bowl, a large castiron or other heavy griddle, a paper towel, a flat wooden spoon or rubber spatula, and a metal spatula.
In a medium-sized bowl, mix together the semolina, yogurt, chile, gingerroot, curry leaves, coriander leaves, and salt. Add the water a little at a time, stirring while you pour. When all the water has been added and the batter is smooth, cover the bowl and let the batter rest for approximately one hour.
To cook the breads, heat a large castiron griddle over medium high heat. Lightly oil the surface of the griddle using a paper towel, and reserve the towel for use between each dosa. When the griddle is hot, pour on one-half cup of the batter. As you pour, move in a circle out from the middle, trying to distribute the batter in as large a circle as possible. Immediately after, use the flat back side of a wooden spoon or rubber spatula to move the batter to cover the gaps, trying again to increase the diameter of the dosa. Try to make a circle 9 to 10 inches in diameter.
Over a medium high heat, the dosa will cook on its first side for one minute and a half. After it has been cooking for one minute, begin to loosen it from the griddle with a sharp-edged spatula. Coax the dosa, don't force it, as it will come off easily from the griddle when it is ready. When ready, flip to the other side.
The second side will cook in one and a half to two minutes, depending on the thickness of the dosa and the heat of the griddle. You can check the dosa by simply lifting a corner with your spatula. It should have nicely browned spots, but not nearly as uniformly brown as the first side. When ready, remove to a plate. Before starting the second dosa, rub the surface of the griddle with the oily paper towel, or if it's particularly dry, add a little more oil. Continue cooking until all the dosas have been made (they can be stacked one on top of the other when they finish cooking), or serve immediately as they are made, flapjack-style.