Boil about 3 handfuls of pasta in seasoned water. Make sure to use enough water and stir so it doesn't stick to the pan.
Heat about 1/2 pint of milk in a pan with a heaped teaspoon of plain flour. When that's heated add 2 handfuls of grated cheese (I used mature Cheddar but the flavour was a little overpowering so it might be better to use a Medium Cheddar instead). Heat until all the cheese is melted and the sauce is thick.
Pile up the pasta and the sauce into an oven proof dish, stir in some tuna and then grate a load more cheese on top!
Pop in the oven for about 20 minutes to melt the cheese and get the top layer of pasta a bit crispy...