Whisk the polenta, 6 cups water and 2 1/2 teaspoons salt together in the insert of a 6-quart Instant Pot® until combined. Turn the pot to the saute setting (see Cook's Note) and bring to a boil. Whisk well, then follow the manufacturer's guide for locking the lid and preparing to cook. Set to pressure cook on high setting for 10 minutes.
After the pressure cook cycle is complete, follow the manufacturer's guide for quick release and wait until the quick release cycle is complete. Be careful of any remaining steam and unlock and remove the lid. Whisk the polenta until smooth.
Whisk in the Parmesan, then the butter. Cover with the lid and set on warm setting until ready to serve.
Settings may vary on your Instant Pot® depending on the model. Please refer to manufacturer's guide.
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