Step 1: Prepare the Slow Cooker
Grease the inside of the slow cooker with non-stick spray or butter to prevent sticking.

Step 2: Cook the Pasta (Partially)
Bring a large pot of salted water to a boil. Add the macaroni and cook for 5 minutes, until slightly tender but still firm (al dente). Drain and set aside.

Step 3: Mix the Sauce Base
In a large bowl, whisk together whole milk, evaporated milk, melted butter, eggs, sour cream, salt, pepper, garlic powder, mustard powder, and paprika until smooth.

Step 4: Add the Cheese
Stir in 3 cups cheddar, 1 cup mozzarella, and ½ cup Monterey Jack (reserve the rest for topping). Mix until the cheeses begin blending into the milk mixture.

Step 5: Combine Everything
Add the partially cooked pasta to the slow cooker. Pour the cheese mixture over it and stir gently to coat all noodles. Sprinkle remaining cheeses on top.

Step 6: Cook to Perfection
Cover and cook on LOW for 2–3 hours, stirring once halfway through. The sauce should be thick and creamy, coating every noodle. Avoid overcooking to prevent mushy pasta.

Step 7: Serve Warm
Stir gently and serve hot directly from the slow cooker.