Begin by bringing a large pot of salted water to a rolling boil over high heat. Once boiling, add the fettuccine or linguine and cook for 8-10 minutes until al dente; it should be tender but still firm to the bite. Once cooked, reserve ½ cup of the pasta water, then drain the pasta and set it aside.

In a large skillet, combine 2 tablespoons of unsalted butter and 2 tablespoons of olive oil, heating over medium heat until melted. Add the sliced leeks, stirring occasionally for 12-15 minutes until they become golden brown and caramelized.

Once the leeks are caramelized, add 8 oz of sliced cremini or button mushrooms to the skillet. Cook for about 6-8 minutes, stirring regularly, until the mushrooms release their liquid and become tender. Then, stir in 2 minced garlic cloves and sauté for an additional minute until fragrant.

Lower the heat to medium-low, then pour in ½ cup of heavy cream, stirring gently to combine with the vegetables. Gradually add 1 ½ cups of shredded Gruyere cheese, stirring continuously until it's fully melted.

Add the drained pasta to the skillet with the cheese sauce, tossing gently to coat the noodles thoroughly. If the sauce seems too thick, slowly add reserved pasta water, one splash at a time, until you reach the desired consistency. Season with salt and freshly ground black pepper to taste.

Plate your comforting Mushroom Gruyere Pasta immediately while it’s still warm. If desired, sprinkle chopped fresh parsley on top for a vibrant touch.