In a small mixing bowl whisk together the sour cream, eggs, milk and all the seasonings well, making sure that the eggs are evenly and completely incorporated.
8 ounces whole milk, 4 ounces sour cream, 1 teaspoon chili powder, ½ teaspoon salt, ½ teaspoon white pepper, ½ teaspoon garlic powder, 2 large eggs
Boil the pasta according to manufacturer's instructions until al dente.
22 ounces elbow macaroni (dry)
Once cooked, drain the pasta (do NOT rinse) and, while hot, add to the large mixing bowl with most of the grated cheese from step 1. Mix to evenly incorporate.
Pour in the milk/egg mixture and mix well until the cheese has started to melt and forms a cheese sauce. There will still be unmelted pieces of shredded cheese. This is fine.
Add a third of the macaroni and cheese to a greased 9x13-inch casserole dish, spreading it in an even layer then add a third of the reserved shredded cheese from earlier.Do this 2 more times.
Bake on the top rack of your oven at 400°F for 30-40 minutes until the top is golden brown and a crust has formed. Allow the macaroni and cheese to rest for 5-7 minutes before serving.
Don't use pre-shredded cheese. They're typically coated with anti-caking agents, which prevent the cheese from melting evenly, resulting in a clumpy and greasy mac and cheese.
Mac and cheese is best enjoyed warm. You can assemble everything ahead of time and bake right before you plan to serve!