8 oz macaroni (usually elbow macaroni, but you can use anything really)
1 cup breadcrumbs (can use up stale bread this way)
3 oz salted butter
2 oz flour
4 oz cheese (cheddar or whatever you prefer)
2 cups milk
(optional) 2 sausages/hot dogs
1 tsp mustard powder
salt and pepper
Boil 8 oz. macaroni (about 10 minutes) till almost cooked, but still on the firm side. Drain these well, and place in a medium size oven-safe serving dish.
While the macaroni is boiling, prepare breadcrumbs by grating or tearing apart bread. Melt about 1 oz salted butter to 1 cup of breadcrumbs and mix together. Set aside in a bowl. (You can make extra breadcrumbs and freeze them for future use.)
Grate 4oz of cheese and set aside.
Measure 2 cups milk and set aside.
Optional: fry or grill sausages and cut into slices when cooked. Sprinkle these over the pasta in the serving dish.
Preheat the oven to 375 F (190 C).
In a saucepan over medium heat, melt 2oz butter and stir in 2 oz. flour. Mix well until the mixture looks mealy, but is not yet turning brown. This is called a "roux".
Add the milk you set aside previously, and stir vigorously with a whisk until the sauce thickens - it will suddenly turn from liquid, to thick sauce. Allow the sauce to simmer gently for about 5 minutes to thicken. If you notice any lumps, whisk the sauce again vigorously until they are gone.
Add a teaspoon of mustard powder and a pinch of salt and pepper to taste. You can also add any other flavorings at this point if you wish, such as spices or beer (if you add liquid, you may need to simmer for a bit longer to thicken again). Add the cheese that you set aside previously, and stir only long enough to melt it.
When the sauce tastes good, pour it over the pasta in the serving dish. Smooth the top with a spatula or spoon, and sprinkle the breadcrumbs over top. Put the dish in the oven for about 10 minutes, until the breadcrumbs are starting to brown slightly.
The cheese sauce is also delicious over vegetables (broccoli, cauliflower, etc.) instead of pasta.