Cut the trimmed leeks in half lengthwise and then slice into ¼ inch thin half-moon shaped slices.

In the same pan, add olive oil and the sliced leeks and onions to the pan. Stir to combine. Season with a generous pinch of salt. Cook over medium-low heat for about 45 minutes or until caramelized. Stir every few minutes. If the pan gets too dry or starts to get too brown on the bottom, pour in a splash of water and scrape with a wooden spoon.

Once caramelized, pour in the white wine. Scrape any stuck bits from the bottom of pan with a wooden spoon and stir to combine with the leeks and onions. Simmer for 2 minutes. Remove the leek and onion mixture to a bowl. Set aside for later.

Cook the pasta in salted water al dente according to package instructions. Reserve 1 cup of pasta water. Make the cream sauce while the pasta cooks.

Use the same pan as the caramelized leek and onions. Add the butter and melt over medium heat. Then add the minced garlic, thyme leaves, and zest of 1 lemon. Stir to combine and cook for 1 minute.

Pour in the heavy cream and season to taste with salt and pepper. Simmer for 5 minutes. Add the parmesan cheese and stir to combine. Simmer for another 3 minutes.

Transfer over the cooked pasta to the cream sauce. Stir until well combined. Add the caramelized leek and onions. Squeeze in the juice of half a lemon. Stir until well combined. Add splashes of pasta water as needed if the sauce is too thick. Taste and season as desired with salt and pepper.

Divide among bowls to serve. Serve with additional lemon juice and parmesan cheese as desired.