Bring 6 cups water and 1/4 teaspoon of the salt to a boil in a large saucepan.
Sprinkle polenta into boiling liquid while stirring with a wooden spoon.
Reduce heat to a simmer and continue stirring 1 to 2 minutes or until water is completely absorbed and polenta is cooked.
Stir in butter and cheese.
Spoon the mixture into an oiled 9x13-inch baking dish.
Let polenta rest for 10 to 15 minutes to firm up while preparing the mushrooms and artichoke hearts.
Heat olive oil over medium-high heat.
Add mushrooms, artichoke hearts, remaining 1/4 teaspoon salt and pepper and cook, stirring frequently, until the mushrooms have released their liquid, about 10 minutes.
Stir in the pasta sauce if using.
To serve, cut polenta into squares and top with mushroom mixture. Garnish with additional cheese or a drizzle of extra-virgin olive oil, if desired.