Blend onions, tomatoes, garlic, ginger, red chili powder, sambhar masala, salt, and coriander leaves in a mixer jar until smooth.

Heat oil in a pan and add mustard seeds, urad dal, asafoetida, and curry leaves. Let them splutter.

Add the blended mixture to the pan and cook for a few minutes. Add a little water if needed and simmer until the chutney thickens.

In a mixer jar, blend rice flour, gram flour, yogurt, soaked red chilies, salt, raw potato, and a little water until smooth.

Add baking soda to the batter and mix well. Adjust the consistency by adding more water if required.

Heat a pan lightly and spread the batter evenly to form a dosa.

Apply oil, butter, or ghee on top and cook on low flame until golden brown.