Add 4 1/2 cups water, 1 tablespoon salt and the olive oil to a medium saucepot and bring to a simmer over medium heat. Whisk in the cornmeal in a steady stream, until it is all incorporated and smooth.
Reduce the heat to medium low and continue to cook at a simmer until the polenta is creamy and fully hydrated, 30 to 40 minutes.
Take the saucepot off the heat and whisk in the butter and Parmesan. Season with additional salt and pepper. Transfer the polenta to a large serving bowl and serve.