firstly, in a large bowl take 1 cup wheat flour, ½ cup rice flour, and 1½ cup water.
whisk and mix well making sure there are no lumps.
add water as required and prepare a thick flowing consistency batter. keep aside.
in a pan heat 2 tbsp oil. splutter 1 tsp mustard, ½ tsp cumin, 1 tsp chana dal, and pinch hing.
add 1 onion, 2 chilli, and saute until the onion softens slightly.
cool the masala slightly, and transfer it to the batter.
add 2 tbsp coriander, ¾ tsp salt, and mix well.
prepare a smooth-flowing consistency batter.
heat the dosa tawa and pour the batter. spread slightly thick making sure the thickness is uniform.
spread some oil and cook on low flame.
flip over and cook both sides until the dosa is cooked well.
finally, enjoy onion tomato dosa with coconut chutney.