Preheat oven to 350 degrees. Add pasta to a rectangular casserole or cake pan. Melt butter in a large skillet over medium heat.
Stir in flour and mix well to form a sort of roux. Reduce heat and continue stirring until mixture thickens.
Stir in cheese about a half cup at a time until smooth (and drool-inducing).
Pour cheese sauce over pasta and cover with foil. Bake covered for 25 minutes, then uncovered for about 10 minutes. Meanwhile, place bacon on a non-stick or greased cookie sheet and bake at the same temperature for about fifteen minutes or to your desired level of crispness.
Remove from oven and place on a plate layered with newspaper to soak up excess grease. Once slightly cooled, crumble up the paper into a little ball. When you unfold it, the bacon should be crumbled into pieces and perfect for sprinkling atop your mac and cheese.
Remove pasta from the oven. Garnish with bacon, if desired, and serve.