Rough sort of recipe - I tend to wing it without very accurate measurements of things:
Serves 4 adults.
Cook 500g of macaroni or other appropriate pasta shape to al dente (I generally go about 2 minutes under the recommended packet instructions)
Fry up 150g of well-diced chorizo and reserve.
Melt 125g of butter in the same pan (there should be some oil left from the chorizo)
Chuck in some flour (I guess about half a cup) and stir to a roux which is roughly the consistency of wet sand
Stir until not lumpy
Add some minced garlic, a level teaspoon of English mustard powder, a pinch of nutmeg, a bay leaf, stir and then immediately start adding the milk to bring the temp down a bit and make sure the garlic doesn't burn in the roux/napalm.
Total of about 2 1/2 pints of whole-fat milk. You have to add it in dribbles to start with and stir vigorously. The roux will glump up into a claggy mess at first but gradually combine with the milk. Once it's a reasonable consistency you can pour in the rest of the milk.
Bring the milk to about 85-90'C (185-195'F) then stir in some grated cheese. I used a mix of Emental, Extra Mature Cheddar, and Monterey Jack.
Season with black pepper
Once that's all thick and cheesy and gooey and nice, return the chorizo to the sauce, then stir in the cooked pasta.
Pour the cheesy pasta into an oven-safe dish or pot, sprinkle breadcrumbs over the top and bake for 20 minutes at 180'C / 360'F.
Check it's bubbling nicely under its breadcrumb hat then grill for 5 minutes to get those breadcrumbs golden.
Let it cool for 5 minutes while whipping up a simple green salad.