Soak chana dal in 1 1/2 cups of water for at least 5 to 6 hours and as long as overnight. Drain the dal, then transfer to a blender. You can add 1 to 2 tablespoons water to facilitate the grinding. You are looking for a grainy mixture like coarse polenta.
Add yogurt, mix well, and set it aside for 8 hours.
Add salt, turmeric, crushed pepper, grated ginger, sugar, and fruit salt. Mix well. Rub little bit of oil inside a small, handleless steel pot or heat-proof bowl (about 5 to 6 inches in diameter). Pour gram dal mixture in this pot.
Place 4 cups water in another large pot and put it on the stove. Turn the heat to medium. Place the dal mixture pot in water. Cover with lid. Cook for 30 minutes.
Take the small pot out. Let cool. Invert the small steel pot onto a plate and tap on the back of the pot. What will come out on the plate is a kind of pie.
Cut this pie into diamond or square pieces (2-by-2-inches).
Heat vegetable oil in a small pot. After 3 to 4 minutes, add black mustard seeds. Once they stop popping, pour this hot oil over the pieces.