Slice the leeks thinly, about 3-4 mm, and rinse thoroughly to remove any grit. Set aside.
Bring a large pot of salted water to a boil and cook your pasta until just al dente, about 8 minutes. Drain and set aside, reserving a splash of pasta water.
Heat olive oil over medium-low heat in a large skillet. Add the sliced leeks and cook gently, stirring occasionally, until they turn soft, golden, and sweet, about 10-12 minutes. The aroma should be sweet and caramelized.
Add the minced garlic to the skillet and cook for about 30 seconds until fragrant, stirring constantly to prevent burning or bitterness.
Stir in the chopped spinach and cook just until wilted, about 1-2 minutes. If using frozen spinach, make sure to squeeze out excess water beforehand to avoid soggy greens.
Combine the drained pasta with the leek and spinach mixture in the skillet. Toss everything together, adding a little reserved pasta water if needed to loosen the sauce and help coat the noodles evenly.
Squeeze fresh lemon juice over the pasta and season generously with salt and freshly ground pepper. Toss again to distribute the flavors evenly.
Let the pasta rest off the heat for 1-2 minutes to allow the flavors to meld and the dish to cool slightly, making it more flavorful and inviting.
Serve the leek and spinach pasta warm, garnished with extra lemon and freshly ground pepper if desired. Enjoy the cozy, caramelized flavors and vibrant greens in every bite!