Read the recipe notes below before starting!
Take the Plant Butter out of the fridge and place in a small bowl to soften. Once softened, add the miso paste and use a fork to cream them together until well combined.
Add the vegetable broth to a saucepan. Once it comes to a rapid simmer, adjust the heat to keep the broth warm/hot at a gentle simmer.
Cook the mushrooms. Heat a large nonstick frying pan over medium-high heat and add 1 tablespoon of the olive oil. Once shimmering, add the mushrooms. Allow to cook undisturbed for a few minutes to develop some browning. Cook for a total of 8-9 minutes, until mushrooms are nicely browned, stirring only occasionally.
Reduce the heat to medium. Add the chopped thyme and HALF of the minced garlic to the mushrooms. Season with 1/2 teaspoon kosher salt. Cook for 2-4 minutes, stirring frequently to prevent burning. Add the creamed miso butter to the pan and stir into the mushrooms. Season with a pinch of salt and pepper and cook for 2 more minutes. Turn off the heat and set the mushrooms aside.
Cook the risotto. Heat a Dutch oven, large nonstick saucepan, or deep sauté pan over medium heat. Add the remaining 2 tablespoons of olive oil. Once hot, add the leeks and remaining garlic and cook for 2 to 3 minutes, until the leeks have just softened.
Add the arborio rice and stir quickly until all of the rice grains are well-coated and the rice smells slightly toasty, 60 to 90 seconds. Pour in the white wine, and stir to scrape any bits stuck to the bottom of the pot, cooking until the wine is nearly all evaporated and the smell of alcohol has dissipated, about 3 to 4 minutes.
Ladle in 1 cup (240 mL) of the warm vegetable broth and stir frequently but not constantly. Once the rice has absorbed the liquid, add the next round of broth, 1 cup at a time. Continue this process stirring about every 30 seconds and adding more broth when most of the liquid is absorbed for about 20 minutes, until the risotto is slightly firm and creamy, but not too soft or mushy.
To test for doneness, you can place the rice on a flat surface and smear downwards with your finger. It should be fairly smooth but you should still be able to see a bit of the white, al dente center of the rice.
Transfer the cooked miso mushrooms to the risotto, and stir to warm through for a few minutes. Remove from the heat, and then stir in vegan Parmesan cheese, if using. Taste for seasonings, adding a bit of salt as needed and some black pepper to season. Garnish with fresh chopped parsley and serve immediately.