Begin by bringing a large pot of salted water to a rolling boil over high heat. Once boiling, add 12 oz of your preferred pasta. Cook for 8–10 minutes until al dente, reserving ½ cup of pasta water before draining.

In a large skillet, combine 2 tablespoons of unsalted butter and 2 tablespoons of olive oil over medium heat. Once melted, add the sliced leeks and cook for 12–15 minutes until caramelized.

Add 8 oz of sliced mushrooms to the skillet, cooking for 6–8 minutes until tender. Stir in 2 minced garlic cloves and cook for an additional minute.

Lower heat and pour in ½ cup of heavy cream, gradually sprinkling in ¾ cup of shredded Gruyere cheese, stirring until completely melted.

Add the cooked pasta into the skillet and toss together. Gradually incorporate reserved pasta water to achieve desired sauce consistency, and stir in remaining ¾ cup of Gruyere until creamy.

Plate the pasta and garnish with freshly chopped parsley before serving immediately.