PREHEAT OVEN TO 350°F.
WHILE MACARONI IS STILL HOT, PLACE IN A LARGE BOWL ALONG WITH THE BUTTER AND 2 CUPS OF THE CHEDDAR.
IN A SEPARATE BOWL, WHISK TOGETHER THE SOUR CREAM, EGGS, HALF-AND-HALF, AND SALT AND PEPPER UNTIL SMOOTH. ADD TO MACARONI AND STIR TO COMBINE.
TRANSFER TO A BAKING DISH, TOP WITH CHEDDAR AND BAKE UNTIL TOP IS GOLDEN BROWN, 30-45 MINUTES.
ENJOY!