Turn the instant pot on saute mode. Heat the oil and add mustard seeds. Let mustard splutter. Add cumin seeds, curry leaves and hing. Saute for 10 seconds.
Add onion, ginger, garlic and turmeric. Cook for two minutes.
Now add the bottle gourd pieces and coat with oil.
Add the tomato, spices, salt and jaggery. Cook for a minute.
Add the tamarind juice and 1 cup of water. Mix well and cancel the saute mode.Close the lid, vent in sealing position.
Change the instant pot setting to pressure cooker or manual mode. Cook on high for five minutes.
Do natural release after 10 minutes. If the pressure is still up even after ten minutes, release the rest of the pressure and open the lid carefully.
Slowly add the butter milk and mix well. Turn on the saute mode and cook for two minutes or until you get the desired consistency.
Turn off the saute mode and garnish with fresh coriander leaves.