Bring a large pot of salted water to a boil, then add your pasta and cook until just al dente, about 8 minutes. Drain, reserving ½ cup of pasta water, and set aside.
While the pasta cooks, clean the leeks thoroughly by slicing into thin half-moons and soaking in cold water if needed to remove any grit. Slice the mushrooms into thin pieces as well.
Heat a large skillet over medium heat, then add 1 tablespoon of butter and a splash of olive oil. Once melted and shimmering, add the sliced leeks. Cook gently, stirring often, until they soften and become translucent, about 8 minutes, developing a tender, slightly caramelized appearance.
Add the sliced mushrooms to the skillet. Cook, stirring occasionally, until they release their earthy aroma and turn golden brown, about 8-10 minutes. If they release excess water, turn up the heat slightly to help evaporate it, ensuring the mushrooms brown nicely.
Lower the heat to medium-low and add the remaining 2 tablespoons of butter. Once melted, stir in the minced garlic and cook for about 1 minute until fragrant and slightly toasted, filling the kitchen with a warm, earthy aroma.
Gently toss the cooked pasta into the skillet, adding a splash of the reserved pasta water. Use tongs to stir everything together, allowing the starchy water to create a silky sauce that coats the noodles evenly. Add more pasta water if needed to loosen the sauce.
Season the pasta generously with salt and freshly ground pepper, tasting and adjusting as you go. Finish with a squeeze of lemon juice if you like a bright note that balances the earthiness.
Remove from heat and sprinkle with freshly chopped parsley or herbs. Serve immediately, enjoying the glossy noodles coated in a fragrant, smoky mushroom and leek sauce that’s warm and inviting.
