This is very simple vegetarian soup.
Though it has buttermilk one can make it vegan by substituting buttermilk by coconut milk.

Supplies

Tomatoes 4-5
Buttermilk 1/2 cup
Ghee/oil/butter 2 teaspoons
Cumin seeds 1/4th teaspoon
Chilli powder 1/2 teaspoon
Chickpea flour 1 tablespoon
Salt as per taste
Sugar 1-2 teaspoon
Curry leaves 4-5

Step 1: Recipe

Boil tomatoes.
Blend/puree the tomatoes, while blending them add chickpea flour to it.
In a pan heat oil/ghee/butter and add cumin seeds to it.
Add curry leaves.
Then add tomato puree.
Once it boils add buttermilk, salt, sugar and red chilli powder.
Bring one boil and it's ready.

For vegan version skip buttermilk and add coconut milk after Turning the stove off. No further boiling after adding coconut milk