1. Bring a large pan of salted water to the boil. Cook the macaroni according to the pack instructions.
2. Meanwhile, in a wide, ovenproof pan, melt the butter. If you don’t have an appropriate pan, just use a regular saucepan here and tip the sauced pasta into a baking dish at the end of step 4. Preheat the grill.
3. Once the butter is foaming, add the flour and cook for 1-2 minutes, stirring. Remove from the heat, then gradually add the milk, whisking until the mixture is smooth. Return the pan to the hob and bring to a simmer, stirring continually, and season.
4. Once the mixture has thickened, remove it from the heat and add both lots of cheese, reserving a handful of Colston Bassett Stilton for the top. Stir until melted. Drain the pasta and mix into the cheese sauce.
5. Mix the cracker crumbs, or breadcrumbs, with the thyme, walnuts, some seasoning and the reserved Colston Bassett to make the topping, and scatter on top of the pasta. Grill for 3-5 minutes, or until golden and crunchy 

https://www.sainsburysmagazine.co.uk/recipes/mains/stilton-mac-and-cheese