Cook spaghetti according to package directions; drain and set aside.

In a large skillet, heat olive oil over medium heat. Add sliced leeks and cook until soft, about 5–7 minutes.

Add minced garlic and cook for 1 minute until fragrant.

Pour in heavy cream, bring to a simmer, and cook for 3–4 minutes.

Stir in Parmesan cheese, salt, and pepper.

Toss cooked spaghetti into the sauce until well coated.

Serve hot, garnished with fresh parsley if desired.