Preheat oven to 180C/Gas 4.
1) In a large pot, bring water to the boil. Season water with salt and cook macaroni until al dente, about 10 minutes.
2) Drain pasta and place in a large bowl and while pasta is still hot add all the cheese.
3) In a separate medium bowl, using a whisk, combine the soured cream, butter, eggs, salt, pepper, and milk and add to the macaroni mixture.
4) Spray casserole dish with nonstick and pour macaroni mixture into the dish. Bake for 30 to 45 minutes or until golden brown. Top with additional cheese, if desired.