Finely chop the onion and tomatoes.

Add the chopped onion and tomatoes to a blender, then add the dried red chilies and garlic. Blend until smooth.

Heat oil in a pan. Add the mustard seeds, and when they start to pop, add the curry leaves. Then add the onion-tomato paste, 2 teaspoons water, and mix well. Cook for a few minutes.

When the oil separates, turn off the heat. Transfer to a bowl and serve with dosa, idli, or uttapam.