There is no doubt in my mind. If you want creamy mac'n'cheese, under no circumstance should you bake it. All throwing it in the oven does is dry it out. I have baked mac'n'cheese many a time in attempt to see why so many other recipes call for doing so, but have yet to see the appeal.
My conclusions from fiddling around with mac'n'cheese over the years:
Butter - a higher ratio of butter in the roux tends to better help lubricate the noodles with cheese sauce.
Mustard - a necessary ingredient for a full flavor profile, but too much ruins the dish.
Egg - a completely unnecessary ingredient that is simply a pain to add.
Heavy whipping cream - Substituting this in place of some of the milk makes for a richer mac'n'cheese.
Cheese - While I do not always freshly grate my own cheese, my sauce is definitely grainy if I don't. Pre-shredded cheese has a preservative coating that does not allow it to melt down smoothly.
1 stick butter (½ cup)
¼ cup flour
1 ½ cups heavy whipping cream
1 ½ cups milk
1 tsp ground mustard
1/2 tsp pepper
1 tsp salt
1+ tsp seasoned salt (or more regular salt) to taste
3 cups shredded cheddar*
1 LB noodles
Cook noodles according to package instructions.
Melt butter in medium saucepan.
Add flour and whisk to combine.
Bring roux to boil and cook for 1 minute, whisking continually to avoid burning.
Stir in heavy cream, milk, mustard, pepper and salt.
Bring to boil to thicken sauce; stir frequently to avoid burning.
Melt shredded cheese on low heat.
Taste, and add more salt if desired. (I typically add at least 1 tsp of Lawry's salt at this point.)
Pour sauce over cooked, strained noodles.
*I usually use 2 cups cheddar and one cup of another type of cheese to give the sauce a more rounded flavor if I have it. (Brick cheese and gouda are my top picks.)
If your cheese sauce is grainy, it may be due to the quality of cheese. Pre-shredded cheese has preservatives and anti-caking agents that inhibit its ability to melt as smoothly. For best results, shred your own cheese.
If anyone has any good tips for reheating leftover mac'n'cheese drop it in the comments below! The best I have found is throwing it in a pot on the stovetop and adding a little milk to try to rehydrate it a bit.