Prep the slow cooker: Lightly grease the insert with butter or nonstick spray. This helps prevent sticking and makes cleanup easy.

Cook the pasta halfway: Boil the macaroni in salted water for about 4–5 minutes. You want it undercooked—firmer than al dente. Drain well. This prevents mushy noodles after slow cooking.

Combine the liquids: In a large bowl, whisk together evaporated milk, whole milk, melted butter, dry mustard, garlic powder, onion powder, paprika (if using), and a generous pinch of salt and pepper.

Add cheeses: Stir in the cream cheese cubes, cheddar, Monterey Jack, and Parmesan. It won’t be fully smooth yet—that’s okay.

Load the slow cooker: Add the partially cooked macaroni to the slow cooker. Pour the cheese mixture over the top and stir to coat the noodles evenly.

Cook low and slow: Cover and cook on Low for 1 hour. After 1 hour, open, stir well, and check the texture. If needed, add a splash of milk. Continue cooking on Low for another 30–60 minutes, stirring once more halfway.

Adjust and serve: When the sauce is thick and creamy and the pasta is tender, taste and adjust seasoning. If you like it cheesier, stir in an extra handful of shredded cheddar until melted.

Keep warm: Switch to Warm for up to 1–2 hours, stirring every 20–30 minutes to maintain creaminess.