Mix all veggies, chillies and pistachios.Pressure cook for 7-8 whistles.
Blend the above mixture to a smooth paste.
Heat butter in a pan. Add cumin seeds. Once they splutter, add the paste along with milk and required water.
Once the mixture starts boiling, add sugar and salt.
simmer for 5 minutes and switch off.
Garnish with chopped onions, pistachios and coriander leaves.
Notes
Since I added green chillies, I did not use pepper powder. This is your personal preference. if you have added more water, you can use corn flour to thicken the soup.