Wash rice a few times until water runs clear. Soak rice in plenty of water for at-least 4 hours or overnight. NOTE: Soak the ½ cup of reserve rice in a separate bowl. Add chopped jackfruit into a blender jar, add ¼-½ cup of water and blend until smooth. Remove jackfruit puree into a bowl.
Drain and add 1 cup rice and ¼ cup water into the same blender jar and blend until the rice is very smooth and no grits remain. Add rice batter into the bowl with jackfruit puree.
Add ¼ cup water into the blender jar, swirl and add the water into the batter.
Add salt to taste and mix well. The batter will be thick.NOTE: Almost like a cake batter consistency. Thickness can range from idly batter-regular dosa batter consistency. Next, drain the reserve ½ cup rice and add into the same blender with 1/8 cup water and blend to a smooth paste. Reserve this batter separately in a bowl, to be used only if the batter needs more rice.
Heat a tava/griddle, preferably cast iron on medium heat. If cast iron griddle needs to be greased, wipe away any excess oil or the jackfruit batter will peel away when being spread on the tava.
When the griddle is hot, pour a ladleful of the batter in the center and use the ladle to spread the batter. Use a circular motion to spread the batter from center to the sides, spreading it as thin as possible. Cover the griddle/tava with a lid.
After 30 seconds, remove the lid and spread ¼ tsp coconut oil on the dosa. When you see the bottom starting to brown, using a thin spatula peel the dosa from the griddle. Note: If you like soft dosa, they can be peeled as soon as they are cooked, if you like them crispy, let them start to brown before peeling. If the dosa is easily removable from the griddle and does not stick, you do not need to add the reserve batter. If the dosa does stick to the griddle and is hard to peel off, add the reserved rice batter into the dosa batter and mix well. Continue making dosas.