Bring the water, chicken bouillon, and 1 tbsp salt to a boil. Add the pasta and cook until al dente, about 8 minutes.
Drain the pasta and return it to the pot. Add 4 tbsp butter and stir to coat the pasta.
Add the shredded cheddar cheese and stir to combine.
In a separate bowl, whisk together the half and half, 1 cup sour cream, and the eggs. Season with the garlic powder, onion powder, paprika, 1 tsp salt, and black pepper.
Grease a cast iron skillet or baking dish with butter. Layer half the pasta mixture in the pan, then pour half the custard mixture over top. Repeat the layers.
Top with additional shredded mozzarella and cheddar cheese.
Bake at 350°F for 30-40 minutes, until golden brown and bubbly.
Let rest for 15 minutes before serving.
