Begin by cooking the pasta in generously salted boiling water, stopping one minute before it's fully tender; keep a cup of the pasta water and then drain.
Pound the chicken breast to an even thickness of about 1 to 1.5 centimeters using plastic wrap and a rolling pin.
Season the chicken on both sides with salt and pepper, then coat it lightly with flour.
Heat the olive oil in a frying pan over medium-high heat and sear the chicken for about two minutes per side, or until cooked through depending on thickness.
Wrap the cooked chicken loosely in foil and set aside to rest.
Melt the butter in the same pan over medium heat and gently sauté the garlic for about a minute, ensuring it doesn’t brown.
Add the rosemary and continue cooking for another 30 seconds.
Pour in the cream and reduce heat to low, allowing it to simmer gently without boiling.
Gradually mix in the parmesan in two or three additions, stirring as it melts into the sauce.
Stir in the black pepper and lemon juice quickly to combine.
Pour in a quarter cup of the reserved pasta water and let the sauce simmer for two to three minutes to thicken slightly.
Toss the cooked pasta into the sauce and let it cook together over low heat for a minute or two.
Slice the rested chicken and either arrange on top of the pasta or mix it through.
Garnish with extra rosemary leaves, freshly grated lemon zest, and more parmesan if desired before serving.
