Prepare Cream Substitute (Optional): If you prefer a dairy-free soup, soak 1/3 cup raw cashews in 2/3 cup boiling water and let them soften while you cook the soup. Blend until smooth at the final stage.
Sauté the Aromatics: Heat olive oil and butter together in a large Dutch oven or heavy-bottomed pot over medium heat. Once melted and hot, add the diced onion, carrots, and celery. Cook, stirring occasionally, until the vegetables soften and become fragrant—about 8 minutes.
Cook Mushrooms and Garlic: Add the sliced mushrooms and minced garlic to the pot. Stir to combine and cook for 6 to 8 minutes, allowing the mushrooms to release moisture and turn a light golden color. This step builds a rich, umami base.
Toast the Wild Rice: Mix the dry wild rice into the vegetable mixture and stir well, coating the grains in the flavors. Let it toast gently for 1 to 2 minutes—this enhances the nutty flavor of the rice.
Season and Simmer: Sprinkle in the poultry seasoning, salt, and pepper. Pour in the vegetable broth and the cup of water. Bring the mixture to a gentle boil, then reduce the heat to medium-low. Cover and simmer for 45 to 60 minutes, or until the rice is tender and cooked through.
Finish with Cream and Cheese: Remove the pot from heat and uncover. Slowly stir in the heavy cream (or cashew cream if using). Gradually add the Parmesan cheese while continuously stirring to prevent clumps. Mix until fully combined, then serve warm.