Into an Instant Pot or other pressure cooker, whisk the polenta, salt, pepper, and 4 cups of water. Press the Saute' button and bring the mixture to a simmer, whisk again, then seal the pressure cooker according to manufacturer's directions, with the dial turned to Sealing. Cook on high pressure for 9 minutes.
While polenta is cooking, make sure to have your butter and cheese(s) ready to add to the pot. When the timer goes off at the end of the 9 minutes, release the pressure manually and carefully open the lid immediately (In other words, don't get distracted and let the polenta sit too long ;) ).
Using a whisk, large fork or wooden spoon, whisk the polenta until it's homogenous and creamy. Use your utensil to press any lumps against the side of the pan to smooth (there shouldn't be much, but will be a few).
Whisk the 3 tablespoons of butter into the polenta, then gradually add the cheese, whisking until melted. Taste and season with more salt if needed.
For Cacio e Pepe polenta, add A LOT more pepper to the mixture, stir and then serve in individual bowls with more pepper and shredded cheese on top.
For polenta to be served with marinara, pesto or both, you may skip the step to add more pepper, but I still add some. Scoop the polenta into individual bowls, add a swirl of marinara sauce and/or pesto sauce. Top with more shredded cheese and chopped fresh basil leaves.