Cook pasta in well-salted boiling water, undercooking by 1 minute. Reserve 1 cup of pasta water, then drain.
Flatten the chicken breast to even thickness. Season with salt and pepper, then dust with flour.
Heat olive oil in a pan over medium-high heat and cook chicken for about 2 minutes per side or until done. Wrap in foil and set aside.
In the same pan, melt butter over medium heat. Add garlic and cook gently for 1 minute without browning.
Add rosemary and cook for 30 seconds.
Pour in cream and bring to a gentle simmer.
Add parmesan in batches, stirring until melted between additions.
Stir in black pepper and lemon juice.
Add ¼ cup reserved pasta water and simmer for 2–3 minutes until slightly thickened.
Add pasta and toss well. Let it cook gently for 1–2 minutes.
Slice chicken and serve on top or mix into the creamy chicken pasta.
Finish with lemon zest, extra rosemary, and more parmesan if desired.