My mac & cheese is Meg's recipe (thank you Meg!):
Prep (boil to al dente) about 500g (maybe a bit less) pasta shape of your choice.
Grate block of Red Leicester or Double Gloucester cheese (about 250-300 g size).
Melt 3 Tablespoons butter in a saucepan & add 3 Tablespoons flour to make a roux. Cook it, stirring constantly, until it browns just a bit. Add about 1 1/2 cups milk - slowly, a bit of milk at a time, stirring constantly to dissolve the roux bits & not be lumpy. Season with salt & pepper. When that's all smooth, and the milk gets steamy, start dumping in the grated cheese & stirring it gradually in until all melted. Add a bit more milk if you think it's too thick.
Prepare a Pyrex or similar baking dish - butter it. Mix the cheese sauce together with the pasta and tip all of it into the baking dish. You could top it with some buttery bread crumbs if you wanted, which is very nice - but I often can't be bothered for that.
Into the oven, about 180 C (160 C fan oven), for about 20-30 minutes, until all bubbly & top is golden. Much better than any mac & cheese I ever ate out of an instant box mix.
(this is not healthy food - it has a LOT of cheese in it!)