Bring water and salt to a boil in a large saucepan; pour cornmeal slowly into boiling water, whisking constantly until there are no lumps.
Reduce heat to low and simmer, whisking often, until cornmeal 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.
Turn off heat and gently stir 2 tablespoons butter into polenta until butter partially melts.
Garlic, Mushrooms, Spinach and Beets
Saute mushrooms and garlic in 1 tbsp. olive oil for five minutes.