Boil your Ditalini pasta according to the package directions, reserve one cup of the pasta water before draining the pasta in case you need to thin out your cheese sauce.
In a pan, melt your butter on low heat.
Add your flour to the pan with the butter, disperse the flour all over the pan instead of dumping it in one spot.
Use a whisk and whisk the butter and flour together. It may clump up a little bit that is ok.
Whisk it for just a minute or two to cook out the raw flavor of the flour.
Add the milk a little at a time, about ¼ cup at a time, whisking constantly to work out the lumps of flour.
The mixture should be smooth and simmering enough to thicken, but not boiling.
Add your mustard and all your seasonings, whisk, taste and adjust seasonings.
Add the cheese a handful at a time and fold in with a spatula, stirring until the cheese melts, then add more and repeat.
Once the cheese mixture is smooth, keep it on the lowest heat if your pasta is still cooking.
When your pasta is cooked, drain it, reserve a cup of the pasta water, add all of your pasta to the cheese sauce and toss to coat.
If your cheese sauce is too thick, add a little of the pasta water at a time to smooth out your sauce.
Serve immediately. Makes great leftovers, but it will not be as smooth and creamy as it is when you first serve it.
