Begin by bringing a large pot of salted water to a rolling boil. Add 12 ounces of fettuccine or linguine and cook for about 8 to 10 minutes, or until al dente. Once cooked, reserve ½ cup of the pasta water for later use, then drain the pasta thoroughly in a colander.

In a large skillet, melt 2 tablespoons of unsalted butter and heat 2 tablespoons of olive oil over medium heat. Add the sliced leeks, stirring occasionally for about 12 to 15 minutes, until they become soft and golden brown.

Once the leeks are caramelized, add 8 ounces of sliced cremini or button mushrooms to the skillet. Cook for 6 to 8 minutes, stirring frequently until the mushrooms are tender and slightly browned. Incorporate 2 minced garlic cloves, cooking for an additional minute until fragrant.

Lower the heat and pour in ½ cup of heavy cream while stirring slowly. Gradually add ¾ cup of the shredded Gruyere cheese, continuing to stir until it melts into a creamy sauce, taking about 2-3 minutes.

Gently fold the drained pasta into the skillet with the cheese sauce. Toss everything together, ensuring each strand of pasta is generously coated in the creamy mixture. If the sauce is too thick, add a splash of the reserved pasta water.

Plate your creamy caramelized leek and mushroom Gruyere pasta, and sprinkle with freshly chopped parsley for a touch of brightness. Serve immediately.