Bring a large pot of well salted water to a boil and cook the pasta, stopping one minute before it’s fully done. Keep a cup of the pasta cooking water and drain the rest.
Place the chicken breast between two sheets of plastic wrap and gently pound it to a uniform thickness about 1 to 1.5 cm.
Season both sides of the chicken breast generously with salt and pepper and lightly coat with flour.
Heat olive oil in a frying pan over medium-high heat and cook the chicken for about 2 minutes on each side, or until cooked through if thicker.
Wrap the cooked chicken loosely in foil and set it aside to rest.
Melt butter in the same pan over medium heat, then add the chopped garlic and cook gently for about 1 minute without letting it brown.
Add fresh rosemary leaves and stir for another 30 seconds to release their aroma.
Pour in the cream and lower the heat so the mixture simmers very gently, avoiding any boiling.
Gradually stir in the parmesan cheese in two or three additions, allowing it to melt fully each time.
Mix in black pepper and lemon juice quickly to blend the flavors.
Add about ¼ cup of the reserved pasta water and let the sauce simmer gently for 2 to 3 minutes until it thickens slightly.
Toss the drained pasta into the creamy sauce and let everything heat together for a couple of minutes while gently bubbling.
Slice the rested chicken and serve it on top of the pasta, or mix it through if preferred.
Finish with extra rosemary leaves, fresh lemon zest, and additional parmesan if desired.
