In a large pan, drizzle the olive oil over medium heat.
Add the onion and cook, stirring often, until softened and translucent.
Gently toss in the mushroom slices and cook, stirring only occasionally, until darkened and beginning to soften.
Stir in the garlic and thyme. Season with salt and freshly ground pepper.
Once fragrant, add the rice and toss until lightly toasted, about 2-3 minutes.
Pour in the wine and cook until absorbed by the rice.
Add 1/2 cup (120 milliliters) of the vegetable broth and continue to cook, stirring frequently, until most of the broth has been absorbed.
Add another 1/2 cup (120 milliliters) of broth, repeating the process of adding broth and stirring until absorbed, until the rice is tender, al dente, and the mixture is creamy.
Stir in the butter, then remove from heat.
Stir in the Parmesan, season to taste with more salt and pepper if needed, then serve immediately with a sprinkling of additional Parmesan and fresh parsley.