You want it less than al dente because the pasta will continue to cook in the oven. Rinse, drain and put into a 3-quart ovenproof casserole dish. Set aside.
Next, add the butter, when melted whisk in the flour and cook while stirring for about 1 minute.
Whisk in the milk a little at a time. It will clump up a bit at first, this is ok!
Then add the half and half a little at a time while whisking constantly.
You might think that there is too much sauce but it's perfect after it is baked.