Creating your Mouthwatering Mushroom Polenta Casserole is easy when you follow these steps:

1. Preheat Oven: Preheat your oven to 375°F (190°C).
2. Cook Polenta: In a medium saucepan, bring vegetable broth to a boil. Gradually whisk in the polenta and reduce heat to low. Stir frequently until thickened, about 5–7 minutes.
3. Saute Vegetables: In a large skillet, heat olive oil over medium heat. Add diced onion and cook until translucent. Stir in minced garlic and cook for an additional minute.
4. Add Mushrooms: Add sliced mushrooms, thyme, salt, and pepper to the skillet. Sauté until the mushrooms soften and release their liquids, about 8-10 minutes.
5. Combine Mixtures: Once the polenta is ready, mix it into the skillet with the mushroom mixture. Stir until well combined.
6. Add Cheese: Stir in half of the mozzarella and half of the Parmesan cheese until melted and evenly incorporated.
7. Transfer to Baking Dish: Pour the mixture into a greased 9×13-inch baking dish, spreading it evenly.
8. Top with Cheese: Sprinkle the remaining mozzarella and Parmesan cheese over the top.
9. Bake: Bake in the preheated oven for 20-25 minutes, or until the cheese is melted and golden brown.
10. Garnish: Once out of the oven, let it cool for a few minutes. Garnish with fresh parsley if desired before serving.

Follow these steps to create this comforting dish, and you’ll soon enjoy a delicious meal.