Cook the pasta in salted water according to the instructions on the packet.
Heat the butter in a saucepan and sweat the flour in it lightly. Deglaze with the broth and cream and bring to the boil, stirring constantly. Simmer for a few minutes, if the sauce is too thick, add some more cream or broth. Crumble in the feta and season with salt and pepper.
Drain the pasta and serve immediately with the sauce.