Slice the leeks into thin rounds, about 5 mm thick, and rinse thoroughly under cold water to remove any dirt. Set aside.
Heat a large skillet over medium-low and add 2 tablespoons of olive oil. Once shimmering, add the sliced leeks with a pinch of salt. Cook gently, stirring occasionally, until they soften and turn translucent, about 10 minutes. The aroma should become buttery and sweet.
Add the sliced mushrooms to the skillet. Increase the heat to medium and cook, stirring occasionally, until they release their juices and darken to a deep, glossy brown, about 8 minutes. They should smell earthy and rich.
Meanwhile, bring a large pot of salted water to a boil. Add the pasta and cook until just al dente, about 8-10 minutes. Reserve a cup of pasta water before draining.
Add the minced garlic to the skillet with the leeks and mushrooms. Cook for about 30 seconds until fragrant, stirring constantly. Be careful not to burn the garlic, as it can turn bitter.
Drain the pasta and toss it into the skillet with the caramelized leeks and mushrooms. Add a splash of the reserved pasta water if the mixture seems dry. Stir well to combine, allowing the flavors to meld for 1-2 minutes.
Remove the skillet from heat and stir in the grated Parmesan cheese and lemon zest. Mix until the cheese melts and the zest releases a bright, fresh aroma. Taste and adjust seasoning with salt and pepper if needed.
Serve immediately, garnished with extra Parmesan if desired. Let the pasta rest for a couple of minutes to allow the flavors to settle. Enjoy the comforting, earthy flavors with a hint of brightness from the lemon.
