Pour 4 and a half cups of fresh water in a saucepan and turn on the heat. To this add a small bunch of chopped coriander stems, 1 small onion roughly chopped, 3 cloves of garlic roughly chopped, 1 medium carrot sliced, 1 tablespoon coriander seeds, 1 teaspoon black pepper powder, ¾ teaspoon salt, and ¼ teaspoon turmeric powder. Bring to a gentle boil, reduce the heat and simmer for 5 to 7 minutes. Once cooked, pour the stock into a sieve and collect the liquid in a bowl. Remove all the boiled carrot pieces and set aside. Discard the rest.
Heat 1 tablespoon butter in a saucepan, add finely chopped garlic and fry till light golden and smells aromatic.
To this add finely chopped onion, finely chopped coriander leaves, boiled carrots from the stock, prepared vegetable stock, lemon juice, salt, and pepper if required and finally ½ teaspoon of sugar.
Stir well and once the soup starts to boil, start adding cornflour mixture while stirring. Keep cooking for a couple of minutes and the soup starts to thicken.
Turn off the flame and serve hot with toasted bread.