In a large bowl, whisk together the dry ingredients: flour, brown and white sugar, baking soda, and salt.
In a medium sized bowl, whisk together the wet ingredients: eggs, butter, milk, and vanilla extract.
In the large bowl with the dry ingredients, create a well in the center. Pour into the center of the well your wet ingredients. Mix well.
Add in your mashed bananas to the bread mixture. Mix well.
Pour one cup of water into your Instant Pot. Place the trivet inside.
Spray cooking spray inside each jar. Pour in the banana bread mixture evenly amongst 4 jars (I suggest using large mouth, pint size jars).
Place aluminum foil over each jar. Place each jar on the trivet.
Close the Instant Pot, and close the vent.
Cook on High Pressure for 20 minutes and allow it to release manually (should take about 15 minutes).
Remove the jars carefully from the instant pot using a towel or hot pad. Transfer to a cooling rack. Allow the bread to cool.
Remove the aluminum foil and enjoy! You can eat straight from the jar with a spoon, or turn the jar upside down on a plate, slice, and serve with butter!