In a small saucepan, heat vegetable broth over medium heat. Once simmering, reduce heat to low to keep warm.
In the meantime, heat a large saucepan over medium heat. Once hot, add half the olive oil (1 Tbsp as original recipe is written) and mushrooms. Season with a pinch each salt and pepper and sauté until tender and slightly browned - 3-4 minutes - stirring frequently. Remove from pan and set aside in a small dish.
Heat the same large saucepan over medium heat once more. Once hot, add remaining olive oil (1 Tbsp as original recipe is written // adjust if altering batch size) and leeks. Sauté for 1-2 minutes, or until softened and very slightly browned.
Add arborio rice, and cook for 1 minute, stirring occasionally to coat.
Add dry white wine and stir gently. Cook for 1-2 minutes, or until the liquid is absorbed.
Using a ladle, add warmed vegetable stock 1/2 cup (120 ml) at a time, stirring almost constantly, giving the risotto little breaks to come back to a simmer. The heat should be medium, and there should always be a slight simmer. You want the mixture to be cooking but not boiling, or it will get gummy and cook too fast.
Continue to add vegetable stock, stirring to incorporate, until the rice is 'al dente' - cooked through but still has a slight bite. This whole process should only take 15-20 minutes (time based on original recipe // adjust if altering batch size).
Once the rice is cooked through and al dente, remove from heat and add vegan butter (optional), vegan parmesan cheese, and most of the cooked mushrooms from earlier, reserving a few for serving. Stir to coat.
Taste and adjust flavor as needed, adding a pinch of salt and pepper to taste or more vegan parmesan to enhance the cheesiness.
To serve, divide between serving bowls and top with remaining mushrooms, additional vegan parmesan cheese, and a sprinkle of parsley (optional).
Best when fresh, though leftovers will keep covered in the refrigerator for 2-3 days.