Spray a 4 quart slow cooker insert with cooking spray. Add pasta, butter, evaporated milk, chicken broth, heavy cream, salt, ground mustard, black pepper, and paprika. Stir well to combine.
Smooth pasta into an even layer, trying to press it down into the liquid. Not all of it will be submerged, and that's okay. Cover and cook on LOW for 1 hour.
Remove lid and stir. At first it will be a big clump, but as soon as you start to stir, it will break up easily. Spread back into an even layer again. Cover and cook on LOW another 10-15 minutes or so, or until pasta is chewy. Not crunchy, but not finished cooking either.
Remove lid and add cubed cream cheese and grated cheeses. Stir well, cover and let sit (with the heat off), for 5-10 minutes.
Keep stirring and you'll see a glorious cheese sauce appear! Serve hot.