Spray a slow cooker (4 to 6-quart capacity) with cooking spray. Cook the pasta to al dente and drain. Place the macaroni in the slow cooker, immediately add the butter and stir until melted.
Add the evaporated milk, half & half, whole milk, 3½ cups of the cheddar cheese, the Velveeta, salt and pepper; stir to blend well.
Cover and cook on low for 2 to 3 hours. During the last 15 minutes of cooking, sprinkle with the remaining ½ cup of cheddar cheese. Once done, turn the slow cooker setting to warm until ready to serve. Leftovers can be stored in an airtight container in the refrigerator for up to 4 days.
Pasta - I love using elbow macaroni noodles because they're so classic, but feel free to use whatever pasta shapes you like! I do not recommend adding uncooked pasta to the slow cooker, as it could absorb too much liquid and become mushy.
Butter - Unsalted is called for, but you can substitute salted butter and just use a pinch of salt in the recipe.
Half and Half - If you do not have or cannot get half and half, simply substitute equal amounts of heavy cream and whole milk.
Cheddar Cheese - I recommend not buying packaged shredded cheese, but instead buying a block and shredding it yourself, as it will melt better and produce a creamier cheese sauce. If you like a cheese blend, you can substitute all or part with Colby-jack cheese.
Velveeta Cheese - One of the keys to keeping this mac and cheese ultra-creamy! If you cannot get Velveeta cheese, you can substitute a half pound of American cheese, purchased at the deli counter, and not the pre-packaged slices.
Increasing the Recipe - This recipe doubles and triples wonderfully! A great one for serving to a crowd. You can make a double batch in a 6-quart (or larger) slow cooker; if you want to make more than that, you'll need an additional slow cooker.
Storage - Store leftovers in the refrigerator for up to 4 days.