Step 1: Prepare the Slow Cooker

Lightly grease the inside of a 4-quart or larger slow cooker. This will help prevent the mac and cheese from sticking to the sides.

Step 2: Combine Ingredients

In the prepared slow cooker, combine the uncooked macaroni, 1 cup of the shredded sharp cheddar cheese, the grated American cheese, the cubed cream cheese, and the grated Parmesan cheese.

Step 3: Add Liquids and Seasonings

Pour in the whole milk and evaporated milk. Add the Dijon mustard, paprika, and onion powder. Season generously with kosher salt and freshly ground black pepper to taste. Remember that the cheese will also add salt, so start with a conservative amount and adjust as needed.

Step 4: Stir and Cook

Stir all the ingredients together, making sure the macaroni is submerged as much as possible in the liquid. Cover the slow cooker and cook on low heat for 90 minutes to 2 hours and 30 minutes. Stir the mac and cheese every hour during cooking to prevent sticking and ensure even cooking. The macaroni should be tender and the sauce should be creamy. If the macaroni is still too firm after 2 hours and 30 minutes, continue cooking for an additional 15-30 minutes, checking for doneness every 15 minutes.

Step 5: Finish and Serve

Once the macaroni is cooked through and the sauce is creamy, uncover the slow cooker and stir in the remaining 1 cup of shredded sharp cheddar cheese. Continue stirring until the cheese is completely melted and the sauce is smooth. If the mixture seems too thick, add a splash of additional whole milk until it reaches your desired consistency. Serve immediately, garnished with fresh chives, if desired.