Miso Mushroom and Leek Pasta

1.Bring a large pot of water with 1 teaspoon salt to a boil.
2.Meanwhile, heat oil in a deep 12-inch skillet over medium-high until shimmering. Add the leeks, season with salt and pepper and cook, stirring often, until softened, about 5 minutes. If they look dry at any point, add a drizzle of oil.
3.Add the mushrooms to the leeks, season lightly with salt and pepper, and cook, stirring every 2 minutes, until the mushrooms have browned, about 10 minutes.
4.When the water is ready, add the pasta and cook until al dente. Halfway through the cooking process, reserve 1 cup of water and let cool slightly on the counter. Drain the pasta in a colander.
5.When both the mushrooms and pasta are done, stir the miso into the reserved pasta water until mostly dissolved. Add it to the skillet over medium-high heat along with the pasta, cheese and vinegar, stirring vigorously until a cheesy sauce forms and coats the noodles, 1 to 2 minutes. Remove from the heat and season to taste with more vinegar, if needed.
6.Garnish with the parsley and more cheese; serve with a final drizzle of olive oil.