In a medium saucepan, bring 4 cups of water and 1 teaspoon of salt to a boil.
Gradually whisk in the polenta, stirring constantly to prevent lumps.
Reduce the heat to low and continue to cook, stirring frequently, for about 20-25 minutes until the polenta is thick and creamy.
While the polenta is cooking, heat the olive oil in a large skillet over medium heat.
Add the sliced mushrooms and cook for about 5-7 minutes until they are browned and tender.
Stir in the minced garlic and thyme, and cook for an additional 1-2 minutes until fragrant.
Season with freshly ground black pepper to taste.
Once the polenta is cooked, remove it from the heat and stir in the butter and grated Parmesan cheese until melted and well combined.
If the polenta is too thick, you can add a little more water or broth to reach your desired consistency.
To serve, spoon the creamy polenta onto plates and top with the sautéed mushrooms. Garnish with extra Parmesan cheese and a sprinkle of fresh thyme if desired.