Bring a large pot of well salted water to a boil. Cook the pasta according to the package instructions for al dente. Drain well.
Meanwhile, melt the butter in a large saucepan over medium-high heat. When the butter starts to foam, add in the flour and cook until lightly golden brown. Be sure to whisk constantly.
Slowly pour in the milk, whisking the entire time. You want to be sure to add the milk slow enough so that the flour mixture smooths out and doesn’t clump. If it does clump, don’t worry. Just continue to whisk as you are heating the mixture and letting it thicken. They will smooth out eventually. Allow to thicken about 6-8 minutes.
Remove from the heat and add in the American cheese slices. Whisk together to incorporate. Add in the cheddar cheese. Whisk again until the cheese mixture is smooth. Pour in the pasta. Season with salt and pepper.
This recipe was adapted from a copycat Panera mac and cheese