You need to make a white cheese sauce;


Equal amounts of butter and plain flour. (About 4 Tablespoons of each)
Melt butter, add flour, cook for a couple of minutes.
Add milk, a little at a time and stir after each addition until it thickens. If you add too much milk too soon it will go lumpy and it's hard to get the lumps out. When it is a nice smooth creamy consistency, add grated cheese, a always put tasty and parmesan.
You stir this sauce through COOKED pasta.
If you like you can fry off some onion and or bacon and add that.
I sometimes add peas and corn to the mix.

Put in a baking dish, sprinkle with either just cheese, or breadcrumbs mixed with a little butter.

I am sure if you look on taste . com they'll have a recipe with exact quantities. Sorry i don't have them, i kind of make it up as i go along!