Whisk polenta and 4 cups water in pressure cooker until combined. Season with 1 tsp. salt and several grinds of pepper. Bring mixture to a simmer over medium-high, whisk again, then seal pressure cooker according to manufacturer’s directions. As soon as cooker hits high pressure, set a timer for 9 minutes. When timer goes off, remove from heat and manually release pressure. Carefully open lid and whisk polenta until homogenous and creamy.
Whisk butter into polenta, then gradually add 4 oz. Pecorino, whisking until melted. Taste and season with more salt, if needed, and lots of pepper.
Transfer polenta to a wide shallow bowl and top with more cheese and coarsely grind more pepper over.
4 servings