Preheat oven to 250°F. In a large bowl, combine flour and salt. Make a well in the center and pour in 1 cup of water and the oil. Gradually add remaining 1/2 cup water, continuing to mix until flour absorbs water.
Knead dough until smooth and elastic, about 5 to 8 minutes. Do not add more flour.
Cover with a damp cloth and let rest for 30 minutes.
Divide into 16 equal pieces and roll out each into thin rounds, 6-in to 7-in. in diameter. Use a light dusting of flour if necessary when rolling. Do not stack.
Heat a griddle or skillet over medium-high heat. Place one chapati on the griddle and cook about 10 seconds; flip and cook other side 1 minute. Flip again and cook 1 more minute. Use a folded dry dish towel or paper towel to press down any bubbles that start to rise up, so bread cooks evenly. (Bread should puff up and have an even distribution of brown spots.)
Place on a clean towel or surface and brush top with butter, if desired. Repeat for the remaining chapatis. Keep warm on a baking sheet in preheated oven, loosely covered with foil. Serve warm.