Bring water to a boil in a large pot.
Once the water is boiling add the pasta to the pot.
Cook the pasta for about 3 minutes.
While the pasta cooks, add the butter to the slow cooker and let it melt using the low setting. Or you can melt the butter on the stove top and then add it to the slow cooker. Once the butter is melted, brush the melted butter all over the slow cooker pot.
Drain and rinse pasta with cold water to prevent the pasta from overcooking.
Mix together the eggs, sour cream, heavy cream, milk, buttermilk, salt, pepper, paprika, garlic powder, mustard, and sour cream in a large bowl. Then, add the cheeses (except one cup of the sharp cheddar) to the mixture, and mix well
Add the cooked pasta to the mixture and stir all the ingredients together.
Place the macaroni mixture in the buttered slow cooker (there will be a small pool of butter in the bottom of the slow cooker and that's ok. It actually makes for a great crust.)
Lightly season the top of the macaroni mixture with black pepper.
Cover the slow cooker with it's designated lid and let it cook for 2 hours on low heat.
At the 2 hour mark, add your last cup of shredded cheese to the top of the casserole and let it cook for another 30 minutes.
If you can, let it sit for at least 10 to 15 minutes before serving so that it will settle.