In a large mixing bowl, combine the mashed banana and butter. Stir in the sugars and beat with a hand mixer until combined.
Add eggs, one at a time, mixing in between. Add the vanilla extract and sour cream. Mix until well combined.
Use a spatula to mix in the dry ingredients. You don’t want to overwork the batter.
Spray a 7” round silicon baking pan with non-stick spray or rub lightly with oil. Pour the batter into the pan and cover with foil (slightly raised in the middle to allow the bread to expand.
Pour 1 cup of water into the Instant Pot. Insert the trivet. Place the cake pan on the trivet.
Secure the lid and set the vent to sealing (if necessary for your model).
Set to cook on high pressure for 55 minutes.
Once the cook time ends, allow the pressure to naturally release for 15 minutes, then release any remaining pressure.
Remove the cake pan from the Instant Pot. Remove the foil. Allow bread to cool in the cake pan for 10 minutes.
Once cooled, turn the bread upside down to release it from the pan.