Step 1

Bring water and salt to a boil in a large saucepan; pour polenta slowly into boiling water, whisking constantly until all polenta is stirred in and there are no lumps.

Step 2

Reduce heat to low and simmer, whisking often, until polenta starts to thicken, about 5 minutes. Polenta mixture should still be slightly loose. Cover and cook for 30 minutes, whisking every 5 to 6 minutes. When polenta is too thick to whisk, stir with a wooden spoon. Polenta is done when texture is creamy and the individual grains are tender.

Step 3

Turn off heat and gently stir 2 tablespoons butter into polenta until butter partially melts; mix 1/2 cup Parmigiano-Reggiano cheese into polenta until cheese has melted. Cover and let stand 5 minutes to thicken; stir and taste for salt before transferring to a serving bowl. Top polenta with remaining 1 tablespoon butter and about 1 tablespoon freshly grated Parmigiano-Reggiano cheese for garnish.