Heat your Instant Pot on Sauté, and once it is hot, add the butter and sugar, mixing well. Allow it to caramelize and for the sugar to melt most of the way.
Add in the bananas, cut side down, and let them coat into the sauce, flipping to ensure the bananas are covered in the sauce.
Add 1/4 c water to deglaze, being sure to scrape up anything that might be stuck in the bottom.
Pour in the other 1/4 cup of water, seal the Instant Pot, and cook on low pressure for two minutes, releasing pressure quickly when done.
Open up the Instant Pot and gently mash the bananas to get a uniform purée.