Cook the pasta in plenty of boiling salted water for about 10 minutes. In the meantime peel the garlic and press it through a garlic press. Coarsely chop the walnuts. Wash sage and cut into fine strips, except for a few leaves for garnishing.
Melt butter in a pot. Sauté garlic, sage and chopped nuts in it. Drain the pasta and mix with the walnut and sage butter. Sprinkle with parmesan and serve garnished with the remaining sage.