Cook your pasta in well salted boiling water, undercooking by 1 minute. Reserve a cup of pasta water before draining.
Flatten the chicken breast to an even thickness (about 1-1.5cm), I do this by laying some plastic wrap over the top and hitting with a rolling pin.
Season the breast well with salt and pepper on each side then dust with the flour.
Heat the olive oil in a fry pan over a medium high heat and fry the chicken for 2 mins each side (or until cooked through if yours is thicker).
Lightly wrap in foil and set aside.
Heat the butter over a medium heat and gently fry the garlic for a minute, it shouldn't brown at all.
Add the rosemary and cook for a further 30 seconds.
Pour in the cream and bring to a very gentle simmer (lower the heat if you need, it shouldn't be boiling).
Add the parmesan in 2 or 3 separate lots, mixing and letting it melt in between each addition.
Add the pepper and lemon juice and mix in quickly.
Add ¼ cup of pasta water and let it gently simmer for a 2 - 3 minutes to thicken slightly.
Add the cooked pasta, toss and let it gently bubble away for a minute or two.
Slice the chicken then serve the pasta with the chicken pieces on top or tossed through.
I like to top with some extra rosemary leaves, freshly grated lemon zest and some more parmesan if you wish.