Vegetable broth should be heated over medium heat in a small saucepan. Once simmering, turn down the heat to maintain warmth.
Meanwhile, place a big saucepan on medium heat. When heated, add the mushrooms and half of the olive oil (one tablespoon according to the original recipe; modify if you're changing the amount of servings). Sprinkle with a little salt and pepper, then sauté for 3–4 minutes, stirring often, until soft and beginning to brown. Take out of the pan and place in a small dish.
Once again, preheat the same large pot over medium heat. When heated, add the leeks and remaining olive oil (one tablespoon according to the original recipe; modify if you're changing the number of servings). Sauté until softened and just beginning to brown, about one to two minutes.
Add the arborio rice and simmer, stirring occasionally, for one minute.
Gently whisk in the dry white wine. Cook until the liquid is absorbed, one to two minutes.
With a ladle, slowly add 1/2 cup (120 ml) of warmed vegetable stock at a time while stirring nearly continuously and allowing the risotto to boil for brief intervals. There should always be a gentle simmer and a medium heat setting. The mixture should be cooking but not boiling to avoid sticky cooking and overcooking.
Stirring constantly, keep adding vegetable stock until the rice is "al dente," or cooked through but still slightly crunchy. It should only take 15 to 20 minutes to complete this process (time based on original recipe; modify if changing amount of servings).
After the rice is fully cooked and al dente, turn off the heat and stir in the vegan butter (if using), vegan parmesan cheese, and most of the previously cooked mushrooms (save a few for dishing). To coat, stir.
If necessary, add extra vegan parmesan to boost the cheesiness or a touch of salt and pepper to taste. Taste and adjust flavor accordingly.
When ready to serve, divide across serving bowls and garnish with more vegan parmesan cheese, parsley (optional), and the leftover mushrooms.
Though leftovers will keep covered in the refrigerator for two to three days, they are best when fresh.