In a skillet, sauté the onions and garlic until translucent.
Add the mushrooms and cook until they release their moisture and become golden brown.
In a mixing bowl, combine the cooked wild rice, sautéed vegetables, vegetable broth, heavy cream, and half of the Parmesan cheese. Season with salt and pepper to taste.
Transfer the mixture to a baking dish and top with the remaining Parmesan cheese.
Bake in the preheated oven for 30-35 minutes, or until the top is golden and bubbly.
Let it cool for a few minutes before serving.
Notes:
This casserole can be made ahead and reheated before serving.