My go-to recipe is pretty simple.
A stick of butter and 4 oz of AP flour make the white roux. Cook just long enough to lose the raw flour taste.
Add one quart of whole milk, and whisk until simmering. At this point it should be thickened and you have a bechamel sauce.
Add 1 pound of deli-sliced American cheese, one slice at a time, whisking after each addition. Velveeta is tasty, but it's just not cheese. (Sorry in advance to any offended by this).
At this point, you have something similar to sauce Mornay, except Mornay uses cheddar. Cheddar doesn't melt well, and is notorious for breaking.
Cook one pound of elbow, or fusilli, or the pasta of your choice, about 3 minutes undercooked.
Place in a 1/4 hotel pan lined with butter, and top with panko, or regular crumbs mixed with about 2 tbsp. of butter.
Cook until the top is browned.
This reheats well, and is amazing. Try adding some raw tomato and bacon, diced.
A couple of tbsp. of truffle oil is a game changer too.