Cook pasta in salted boiling water until al dente, 9-11 minutes. Reserve 1 cup pasta water before draining. Set aside.
Heat olive oil in large skillet over medium-high heat. Add sliced beef, season with salt and pepper, and cook 3-4 minutes until browned. Remove and set aside.
Reduce heat to medium. Melt butter, add onion, and cook 3-4 minutes until softened and translucent.
Add garlic and cook 1-2 minutes, stirring constantly, until fragrant and golden.
Pour in chicken broth, scraping up brown bits. Simmer 2-3 minutes until slightly reduced.
Reduce heat to medium-low. Add heavy cream, stir well, and simmer gently 3-4 minutes until thickened.
Stir in Parmesan, whisking continuously until melted and smooth. Keep heat low.
Return beef and juices to skillet. Toss to coat and warm through, 1 minute.
Add pasta and toss until evenly coated. Add reserved pasta water if needed to loosen sauce.
Taste and adjust seasoning. Serve immediately garnished with herbs and extra Parmesan.
Notes
Fresh garlic is essential for best flavor. Slice beef against grain for most tender results.
Don’t let cream boil rapidly or it may break. Keep heat low when adding cheese to prevent graininess.
Reserve pasta water to adjust sauce consistency. The starch helps create silky texture.