In a large pot, add approx 6 cups of water (and 1T salt, optional) to a boil. Note: I use course salt. If using table salt, use less.
Add 3 cups of pasta and cook until al dente. Stir a few times during cooking process to prevent the noodles from sticking together. Drain pasta water from noodles in a colander, but do not rinse. Set pasta aside.
In the same warm saucepan, warm 8oz of the Velveeta and 1 cup of milk over medium heat. Tip: Keep a close eye on the sauce and be sure to stir frequently to avoid scorching.
Once the Velveeta is mostly melted, stir in 1 cup of freshly grated cheddar cheese. Note: its important to use freshly grated cheese as pre-shredded cheese has a coating on it that prevents it from melting well, and may cause clumps.
Add cooked pasta back into the pot and give everything a good stir to combine. Make sure the pasta is completely coated in the cheese sauce.