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. Drain and rinse pasta with cold water to prevent the pasta from overcooking.
Coat the pasta with the melted butter.
Mix together the eggs, sour cream, heavy cream, milk, buttermilk, salt, pepper, paprika, garlic powder, mustard, and sour cream in the slow cooker. Then, add the cheeses (reserve one cup of the sharp cheddar for later) to the mixture, and mix until combined.
Add the cooked pasta to the mixture and stir until combined.
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.
Let it sit for at least 10 to 15 minutes before serving so that it will settle.