1. In a medium frying pan, toast walnuts 2 to 3 minutes over medium heat until lightly browned, shaking pan frequently. Set aside.
2. In a large saucepan, boil cream over medium heat until reduced to about 1 1/2 cups, about 5 minutes; be careful not to let it boil over. Stir in cheese until melted.
3. Meanwhile, cook pasta in a large pot of boiling salted water until tender, 2 to 4 minutes; drain. Pour pasta and sauce into a warmed large bowl and toss together. Sprinkle with walnuts.