Begin by heating 1 1/2 tbsp of oil in a pan.
Introduce 1/2 tsp mustard seeds, 1/2 tsp cumin seeds, and 1/4 tsp fenugreek seeds, and sauté.
Add 2 diced onions and cook until softened.
Incorporate 2-3 green chilies and 1/4 cup of curry leaves, frying for about a minute.
Sprinkle in 1/2 tsp of turmeric powder and 1 tsp of ginger-garlic paste, stirring for another minute.
Integrate 3 diced tomatoes, cooking until they reach a soft consistency. Cover and cook as needed.
Season with 1 tsp of chili powder and salt to taste, mixing well.
Pour in the juice of 20 grams of tamarind along with water as necessary. Allow the mixture to simmer for 3-4 minutes.
In a separate bowl, combine 2 tbsp of Bengal gram flour with 2 cups of water, ensuring a smooth mixture without lumps.
Gradually add this flour-water mixture to the simmering charu, adjusting thickness to your liking.
Sprinkle coriander leaves into the mix and stir.
Allow the charu to simmer for an additional minute. Optionally, introduce 1 tbsp of sambar powder for added flavor.
Be cautious not to let the charu thicken excessively on the stove, as it will naturally thicken upon cooling.