Bring a large pot of salted water to a rolling boil. Add fettuccine and cook according to package instructions, usually about 8–10 minutes. Reserve 1 cup of pasta water, then drain pasta.

In a large skillet over medium-high heat, add olive oil. Season beef with salt and pepper, then sear for 3–4 minutes until browned. Remove and set aside.

In the same skillet, reduce heat to medium and melt butter. Add chopped onions and sauté for 2–3 minutes until translucent. Add minced garlic and sauté for another minute.

Pour in chicken broth to deglaze, scraping up any browned bits. Stir in heavy cream and grated Parmesan, bring to a gentle simmer for 3–4 minutes.

Return cooked beef to the skillet with reserved pasta. Toss to coat, adding reserved pasta water as needed for desired consistency.

Remove from heat and garnish with chopped parsley or basil. Serve immediately, optionally with extra Parmesan.