Fill a large saucepan with water, add a generous pinch of salt and bring to the boil.When the water is galloping, add the pasta and cook until al dente according to the packet instructions.
Meanwhile, pour the cream into a small saucepan and add the cheese, then set over a medium-low heat and stir occasionally until the cheese has almost completely melted. Core the pear(s) and slice finely, then roughly chop the nuts.
Drain the pasta in a colander, reserving a little of the cooking water (roughly 1⁄4 cup), toss in the cheese sauce and reserved cooking water, then, just before serving, toss through the pear and walnut pieces. Add a little black pepper, if you like, and serve immediately.