01 - Heat olive oil in a large skillet or saucepan over medium heat. Add onion and sauté for 3–4 minutes until softened.
02 - Add garlic and mushrooms. Cook for another 5–6 minutes until mushrooms are tender and browned.
03 - Stir in the Arborio rice and cook for 1–2 minutes to lightly toast the grains.
04 - Pour in the wine (if using) and cook, stirring, until mostly absorbed.
05 - Begin adding warm vegetable broth 1/2 cup at a time, stirring frequently. Allow the broth to absorb before adding the next 1/2 cup. Repeat until rice is tender and creamy, about 20 minutes.
06 - When the rice is just about done, stir in the spinach and cook until wilted.
07 - Remove from heat. Stir in Parmesan cheese and butter. Season with salt and pepper to taste.
08 - Garnish with chopped parsley and serve hot.