In a pressure cooker add carrot, ginger, garlic, mint leaves, bay leaf, salt as needed, 3/4 liter of water and pressure cook it for 3 whistle.
Once the pressure remove carrot, tomato and grind to fine mash and add it back to the pressure cooker.
In a pan melt butter. Add onion and cook until it turns translucent. Now add the soup the from pressure cooker, black pepper. Bring this boil and cook for 2 minutes. Now add the milk and bring to a boil and remove from stove.
Garnish with coriander leaves and serve.
If you don't like chunks in your soup you can filter the liquid after you add back the mashed carrot and tomato.
If you want the soup to be thick, dissolve 1 tablespoon (tsp.) of corn flour in water and add to the soup before you remove from heat.