In a medium saucepan, keep the vegetable broth warm over low heat.
- In a large skillet or Dutch oven, heat the olive oil or butter over medium heat. Add the chopped onion and garlic, and sauté for about 5 minutes, until the onions are translucent and fragrant.
- Add the black trumpet mushrooms to the skillet and cook for another 5-7 minutes, until they are soft and have released their moisture. Season with salt and pepper to taste.
- Stir in the Arborio rice and cook for 2 minutes, allowing the rice to lightly toast and absorb the flavors of the mushrooms and onion.
- Pour in the white wine (if using), stirring constantly until the wine is mostly absorbed by the rice.
- Begin adding the warm broth, one ladle at a time, stirring constantly and letting the liquid be absorbed before adding more. Continue adding broth and stirring for 18-20 minutes, or until the rice is creamy and tender but still has a slight bite to it (al dente).
- Once the risotto is done, remove from heat and stir in the fresh lemon juice (if using) and Parmesan cheese for added richness.
- Serve the risotto warm, garnished with fresh herbs like thyme or parsley, and additional Parmesan if desired.