Read the recipe notes below before starting!
Take the vegan butter and miso out of the fridge and place in a small bowl to soften. Once softened, 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 frying pan over medium-high heat and add 1 tablespoon of the olive oil (if using stainless steel or cast iron, use more oil). Once the oil is shimmering, add the mushrooms. Cook undisturbed for a few minutes to develop some browning. Cook for a total of 8 to 9 minutes, until 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 to 4 minutes, stirring frequently to prevent burning. Add the creamed miso butter and stir into the mushrooms, stirring frequently to coat the mushrooms for 2 minutes. Season with a pinch of salt and pepper. Set aside. Cook the risotto. Heat a Dutch oven or heavy-bottomed deep sauté pan over medium heat (note 6). Add the remaining 2 tablespoons of olive oil. Once hot, add the leeks and remaining garlic. Cook for 2 to 3 minutes, until the leeks have just softened.
Add the rice and stir quickly until all the grains are well-coated and the rice smells slightly toasty, 60 to 90 seconds. Pour in the wine, and stir to scrape any bits stuck to the bottom of the pot, cooking until the wine is nearly evaporated and the smell of booze has dissipated, about 3 to 4 minutes. Ladle in 1 cup (240 mL) of 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 has been absorbed.It should take about 20 minutes from the time you add the first ladle of broth, or 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. (note 7).
Add cooked mushrooms to the risotto, and stir to warm through. Remove from the heat, and stir in vegan parmesan, if using. Taste for seasonings, adding salt and pepper as needed. Garnish with chopped parsley and serve immediately.