Shred all blocks of cheese. Do not use pre shredded cheese, as it contains a compound that prevents the cheese from clumping, which also makes it unable to be incorporated into a sauce properly. NOTE: You can sprinkle pre shredded cheese on top of the Mac n cheese at the end as it will melt properly, it just won’t incorporate into a sauce.
In a large saucepan over medium heat, melt the stick of butter. Once melted, sprinkle the 1/3 cup of flour over the butter and constantly whisk as it clumps up. You are now cooking the flour taste out of the mixture by continuing to whisk for 3-4 minutes. Don’t let it burn. Add in the chicken stock while whisking. Begin adding the whole milk, a little at a time continuing to whisk all the time. Once the mixture becomes smooth again, add more milk and whisk again. Keep doing this until you have used all the milk. Continue whisking to allow it to thicken slightly for about another 5 minutes. Add salt and pepper and taste - test the sauce for seasoning.
Once it is the right saltiness for your taste, begin adding in the cheese, a handful at a time, stirring to incorporate each handful. You want a smooth sauce that is not overly thick. Taste test along the way until you achieve the right amount of cheesiness. NOTE: You may not use all the cheese, but do try to use a mixture of all the types. If your sauce gets too thick, you can add more milk or chicken stock to thin.
Boil the pasta noodles separately until done. Drain the noodles and this time (you never do this for other pasta sauces!) but this time you can rinse the noodles in a colander as we do not need any starch to thicken the sauce further.
Add the pasta to the cheesy sauce a little at a time, stirring until you achieve a Mac n cheese that is quite saucy. You want it extra saucy because the time in the oven will thicken it once again. Sprinkle with the pre shredded cheese if desired.
Place in a 375 degree oven for 10-15 minutes, then you can also quickly broil it too for a nice toast on top. But watch it carefully - an overdone Mac n cheese is not desirable. Enjoy!!