Coat the inside of an IP-friendly 1.5 quart casserole with nonstick spray and set aside.
Add 2 tbsp butter to the Instant Pot. Using the display panel select the Saute function.
When butter melts, add onion to the pot and saute until soft, 3-4 Minutes.
In a blender, combine the cream, eggs, flour sugar, 1 2/3 cups of the corn, the remaining 3 tbsp of butter, salt and pepper. Blend until smooth.
Add the cooked onion and the remaining corn and pulse once, just to combine. Pour into the prepared casserole and cover loosely with foil--do not seal.
Rinse out the pot, pour one cup of water in the Instant Pot and insert the steam rack. Carefully lower the casserole on to the steam rack using a foil sling.
Turn the pot off by selecting Cancel, then secure the lid, making sure the vent is closed.
Using the display panel select the Manual or Pressure Cook function*. Use the +/- keys and program the Instant Pot for 40 Minutes.
When the time is up, let the pressure naturally release for 10 Minutes, then quick-release the remaining pressure.
(Optional) Set under the broiler for 4-6 Minutes until lightly browned.
Sprinkle with chives and serve hot.
Notes
*The MANUAL and PRESSURE COOK buttons are interchangeable.