Cook the pasta in a medium pan of boiling salted water according to the packet instructions, then drain, reserving a mugful of cooking water. Melt the cheese in a heatproof bowl above the pasta as it cooks, removing carefully when gooey. Meanwhile, slice the radicchio 1cm thick. Place it in a large dry non-stick frying pan on a high heat to char for 5 minutes, turning halfway. Peel the pears with a speed-peeler, then quarter, core and finely slice lengthways. Toss into the pan, crumble in most of the walnuts, add a splash of pasta cooking water, reduce to a medium heat and pop the lid on, then leave to caramelize slightly. Toss the drained pasta and oozy Gorgonzola into the pear pan with a splash of red wine vinegar, and a splash of reserved cooking water, if needed. Taste, season to perfection with sea salt and black pepper, crumble over the remaining walnuts and drizzle with 1 teaspoon of extra virgin olive oil.