½ cup channa dal
1 ½ teaspoons salt, plus more for sprinkling
1 ½ teaspoons cumin seed, toasted in a hot pan for 1 minute
4 cups flour, plus extra for the bench
1 teaspoon baking soda
2 oz. cold butter (half a stick) cut into small pieces (pea-size)
Vegetable oil for shallow-frying
Bring 2 cups of water and 1/2 teaspoon of the salt to the boil in a saucepan. Rinse the channa dal, then add to boiling water. Simmer for 30 minutes, stirring occasionally.
After 30 minutes, drain off water and reserve dal.
In a spice grinder, grind the cumin seed. Mix ground cumin with reserved dal, and place in food processor. Pulse a few times until the mixture is mashed, but with some whole pieces of dal remaining. Reserve.
Place the flour in a large mixing bowl. Mix with baking soda, and 1 teaspoon of salt. Add enough warm water, blending with your hands, to form a soft dough (2 cups water, or a little less, should do it). Do not knead, or even over-mix. Sprinkle the cold pieces of butter over the dough, and quickly blend in with your hands. Let rest for 5 minutes.
After the rest, divide the dough into 8 balls, then flatten each one slightly. Create a deep depression at the center of each ball, and fill each depression with 1/8 of the dal mixture. Bring the sides of each ball over the center, and twist--forming 8 balls with dal enclosed. Let rest for 2 minutes.
Sprinkle a little flour on a board, and add one of the balls. Flatten the ball, then start rolling with a pin. Your goal is a round pancake, about 10" in diameter, no more than 1/8" thick (the thinner the better). Make sure the roti doesn't stick to the board while rolling; turn frequently. Try to make the roti as even as possible in thickness. Try to keep the dal inside. Repeat until you have 8 uncooked rotis.
Place about a tablespoon of oil on a griddle or large frying pan over medium-high heat. Add one raw roti (or more, if they fit), and cook for 2 minutes per side, turning occasionally. They should have golden-brown blisters on the outside. After removing rotis from pan, salt lightly and hold them under a towel. Repeat, replenishing oil, until you have 8 cooked rotis. Serve warm.