Bring a large pot of salted water to a boil.,

Meanwhile, heat 2 tablespoons oil in a Dutch oven or deep 12-inch skillet over medium-high until shimmering. Add the leeks, season with salt and cook, stirring often, until softened, about 5 minutes. If they look dry at any point, add a drizzle of oil.,

Add the mushrooms to the leeks, season lightly with salt, and cook, stirring every 2 minutes, until the mushrooms have browned, about 10 minutes. (If they are done before the pasta, then adjust the heat to low.),

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 and drizzle with olive oil if done before the mushrooms.,

When both the mushrooms and pasta are done, stir the miso into the reserved pasta water until mostly dissolved. Add it to the Dutch oven or 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.,

Garnish with the parsley and more cheese; serve with a final drizzle of oil.