Cook the pasta in a large saucepan of salted boiling water according to the packet instructions until al dente.
Meanwhile, melt the butter in a frying pan over a medium heat. When it begins to foam and sizzle, stir in the sage and garlic and cook, stirring, for 1–2 minutes until golden. Remove from the heat and stir in the walnuts, cream and Parmesan.
Drain the pasta and stir it thoroughly into the sauce. Season with salt and pepper and serve immediately.