Bring a large pot of salted water to a boil and cook pasta until al dente. Drain and set aside.
In a large skillet, heat olive oil and butter over medium heat. Add sliced leeks and cook until softened and caramelized, about 8 to 10 minutes.
Stir in mushrooms and cook until browned and tender, around 6 to 7 minutes. Add garlic and sauté for another minute.
Deglaze the pan with white wine, scraping up any browned bits, and let it reduce slightly.
Pour in heavy cream and let it simmer until slightly thickened, about 3 to 4 minutes.
Lower heat and stir in shredded Gruyere until melted and smooth. Season with salt and pepper.
Add cooked pasta to the skillet and toss until coated with the sauce.
Serve hot, garnished with fresh parsley.