Start by bringing a large pot of salted water to a rolling boil. Add the spaghetti and cook until just al dente, about 8 minutes. Drain, reserving a cup of pasta water, and set aside.
While the pasta cooks, thinly slice the cleaned leeks, ensuring all grit is washed away. Gently heat 2 tablespoons of olive oil in a deep skillet over medium-low heat, and add the sliced leeks. Sauté slowly, stirring occasionally, until they turn soft and translucent, about 10 minutes, releasing a sweet aroma.
Once the leeks are tender and fragrant, add the crushed garlic to the skillet. Cook for about 1 minute until fragrant, being careful not to let it burn.
Throw in the fresh spinach, stirring gently, and cook for 2-3 minutes until wilted and vibrant green. If the mixture looks dry, add a splash of the reserved pasta water to loosen and create a glossy sauce.
Add the drained pasta to the skillet with the greens. Toss gently with tongs or a wooden spoon to coat all the strands evenly in the leek and spinach mixture. Squeeze the juice of half a lemon over the pasta, then season with salt and pepper to taste.
Check the dish for seasoning; adjust with more salt, pepper, or lemon juice if needed. If it seems a little dry, stir in a bit more reserved pasta water until it’s glossy and well-coated.
Serve the leek and spinach pasta immediately, garnished with a drizzle of olive oil if desired. Enjoy the warm, tender greens and flavorful pasta while still fresh and fragrant.
