Cook pasta according to package directions. Drain and set aside, leaving it in the pot.
Preheat oven to 350 degrees F.
In a saucepan, combine cheese soup, cubed cheeses, Velveeta cheese, milk, and cream.
Heat on medium-low until all cheeses are melted. Sauce should stick nicely to the spoon, without running off too easily. If you find the sauce too thick, add more milk. If you find the sauce too thin, add more Velveeta.
Add ground mustard, pepper and Tabasco sauce (if using). Measurements are approximate. Add more or less according to your taste. Stir thoroughly.
Add parsley to the sauce.
Pour sauce over the pasta noodles and blend together.
* If you are using the onions and/or bacon pieces, blend those ingredients in with the pasta and cheese sauce now.
Pour pasta and cheese mixture into large casserole dishes. No need to grease the casseroles. Use casserole dishes that will allow your mac and cheese to be 3 inches deep. I use my two largest casserole dishes for this.
Sprinkle tops with bread crumbs and additional pepper if desired.
Cover tops with shredded cheese.
Loosely tent the casseroles with foil, so that they are covered, but not touching the cheese topping.
Place in oven and bake for 20 minutes at 350 degrees.
Remove foil and increase heat to 450 degrees. Bake or broil for an additional 10 minutes to get a nice crunchy/cheesy topping.