Place vegetable broth in a medium saucepan over low heat, keeping it at a gentle simmer.

In a large skillet, heat olive oil over medium heat; cook mixed mushrooms and garlic until golden brown, about 5–6 minutes.

Add butter to the same skillet, then cook finely chopped onion until translucent, around 3–4 minutes.

Stir in arborio rice, coating each grain in the buttery onion mixture; cook for 2 minutes.

Pour in white wine and simmer until fully absorbed, about 1–2 minutes.

Ladle in a cup of warm broth; stir gently until mostly absorbed. Repeat for 18–20 minutes.

Return sautéed mushrooms to the rice, folding gently until creamy.

Remove from heat, stir in grated Parmesan cheese until silky smooth and season with salt and pepper.