Heat the olive oil in a large pot over medium-high heat. Add the diced onion and cook for a few minutes until it becomes tender.

Introduce the sliced mushrooms and garlic to the pot. Cook while stirring until the mushrooms release their moisture, about 5 minutes.

Remove the lid and stir in the arborio rice. Sauté the rice with the mushroom mixture for a couple of minutes.

Pour in 3 cups of vegetable broth. Stir well, cover the pot, and let it simmer for approximately 15 minutes until most of the liquid is absorbed.

Add another 1 1/2 cups of vegetable broth, stir again, cover, and continue simmering for about 10 minutes.

Finally, add the remaining 1 1/2 cups of vegetable broth. Stir, cover, and cook for an additional 5 to 10 minutes, until the rice has absorbed most of the liquid.

Once the rice is creamy and the broth is mostly absorbed, remove from heat. Stir in the plant-based butter. Season with salt and black pepper to taste.

Garnish with chopped parsley and a sprinkle of ground black pepper. Optionally, top with vegan Parmesan cheese if desired.