Blend together the yogurt, besan, water, cayenne, sugar and salt. Don't let it get too frothy, just mix until everything is mixed.
Turn your Instant Pot onto Sauté on high. When the display reads HOT, add your ghee or oil. When the ghee is hot and shimmering, add the cumin and mustard seeds and let them sputter for 10-20 seconds.
Add the serrano pepper and ginger as well as the turmeric.
Pour in the blended yogurt mixture and seal the Instant Pot.
Cook on SOUP setting for 4 minutes, and allow the pressure to release naturally for 10 minutes. Release remaining pressure.
We're using the SOUP setting so as to not allow the yogurt to come to a vigorous boil which could cause it to separate.
If you find your pot is not coming to pressure, mix in a little additional water. I wish I could be more precise, as I usually am, but feedback from readers has shown that the yogurt they start out with makes a huge difference. If the yogurt was too thick to start with, you will need to add more water.
Do not use Greek Yogurt for this. If you do, add more water.
The final consistency you want is that of a thin pancake batter. So start out thinner than that, and once it cooks it should thicken up like a soup.