Cook the pasta according to the package directions until al dente (should still have a little 'bite' to it.)
Spray a 4-quart slow cooker with nonstick cooking spray.
Place the cooked macaroni into the slow cooker.
Add the butter and stir until coated.
Pour in evaporated milk, half & half, 2 cups shredded cheddar cheese, cubed American cheese salt & pepper. Stir to blend.
Cover and cook on low for 1 1/2 to 2 hours (gently stir occasionally as it cooks.)
During the last 15 minutes of cooking, top with remaining cup of shredded cheddar cheese. Cover and allow cheese to melt.
Once done, turn the slow cooker to the warm setting until ready to serve.
Just go to your grocery store's deli counter and ask for 3/4 pound of white American cheese. Tell them you don't want it sliced, just a big block. Leftovers can be stored in an airtight container in the refrigerator for up to 4 days.