Preheat your oven to 350°F and lightly grease a 9x13 baking dish.

Prepare the wild rice according to the package directions. Once cooked, transfer to a large mixing bowl.

In a large skillet over medium-high heat, cook the sausage until browned and no longer pink. Drain off any excess fat, then add the sausage to the bowl with the rice.

In the same skillet, add the diced onion and sliced mushrooms. Sauté for 5–7 minutes, until soft and golden. Season with salt and pepper to taste, then add them to the bowl with the sausage and rice.

Wipe out the skillet and melt the butter over medium heat. Whisk in the flour and cook for 1–2 minutes to form a roux. Slowly whisk in the chicken broth and heavy cream, stirring constantly until the sauce is smooth and thickened. Stir in the sage and thyme, and season again with salt and pepper. Pour the sauce over the sausage mixture and stir until everything is well coated.

Transfer the mixture to your prepared baking dish and bake for 20 minutes, or until hot, bubbly, and golden around the edges.

Let the casserole rest for a few minutes before serving. Garnish with a sprinkle of fresh herbs if desired.