Steps
1. In a saucepan, heat the vegetable broth over low heat and keep it warm.
2. In a separate pan, heat olive oil and butter over medium heat. Add the chopped onion and sauté until softened and caramelized, about 10 minutes.
3. Add the sliced mushrooms to the onions and cook until they're tender.
4. Stir in the Arborio rice and cook for 1-2 minutes, allowing the rice to absorb the flavors.
5. Gradually add the warm vegetable broth, one ladle at a time, stirring continuously until the liquid is absorbed before adding more.
6. Continue this process until the rice is creamy and al dente, about 18-20 minutes.
7. Season with salt and pepper to taste, and stir in the Parmesan cheese if using.
8. Serve warm, garnished with additional Parmesan if desired.