Bring a large pot of salted water to a boil and cook your pasta until al dente, about 10 minutes. Drain, reserving about 1/4 cup of the pasta water, and set aside.
While the pasta cooks, thinly slice the washed leeks and chop the mushrooms into bite-sized pieces. Mince the garlic finely.
Heat the olive oil in a sauté pan over medium heat. Add the sliced leeks and cook gently, stirring often, until they become translucent and slightly caramelized, about 8-10 minutes. They should smell sweet and buttery.
Add the sliced mushrooms to the pan. Sauté until they release their juices and turn golden, about 7-8 minutes, stirring frequently to develop a smoky aroma.
Push the vegetables to the side of the pan, then add the minced garlic. Cook for about 30 seconds until fragrant, making sure it doesn’t burn, then stir everything together to combine.
Pour in the reserved pasta water to loosen the mixture slightly, then add the drained pasta to the pan. Toss everything gently, letting the sauce coat the noodles evenly. Adjust seasoning with salt if needed.
Finish by squeezing in the lemon juice for brightness, then sprinkle the freshly grated Parmesan over the top. Toss gently again to distribute all the flavors and melt the cheese slightly.
Serve immediately on warm plates, garnished with extra Parmesan if desired. Let the pasta rest for a minute so the flavors can meld before enjoying this cozy, earthy dish.