Start by cooking your large elbow pasta according to the package instructions. You want it al dente since it will continue to cook in the slow cooker. Drain and set aside.
In a large bowl, combine the cooked pasta, slivers of butter, pieces of cream cheese, salt, black pepper, cayenne pepper, and paprika. Mix well to ensure everything is evenly distributed.
Pour in the evaporated milk, whole milk, and heavy cream into the pasta mixture. Stir until combined, and the pasta is well coated.
Fold in the freshly shredded sharp cheddar cheese and pepper jack cheese, ensuring the pasta is enveloped in the cheesy goodness.
Transfer the pasta mixture into your slow cooker. Cover and cook on low for about 2 to 3 hours, stirring occasionally. Keep an eye on it to make sure it doesn't overcook; you want that perfect creamy consistency.
Once it’s done, give it a good stir, and it’s ready to serve! Enjoy your Slow Cooker Ultra Creamy Mac and Cheese straight from the slow cooker or transfer it to a serving dish for a more polished presentation.