The egg biscuit is the Southern breakfast sandwich reduced until only the bread matters. Strip away the country ham, the sausage, the sawmill gravy, and what is left is an egg on a split buttermilk biscuit, which means the biscuit is no longer a counter to a salty meat but the entire event. The defining decision is that absence. With nothing salty and fatty layered in to lean on, the sandwich stands or falls on the quality of the biscuit and the doneness of the egg, and the egg's only job is to be a soft, mild filling that lets the bread be the point.
The craft is almost all in the biscuit. A buttermilk biscuit is built tender and short, its crumb layered and rich with fat, baked so the outside takes a faint crust while the inside stays soft enough to compress around a filling without crumbling apart in the hand. Split warm, it has a tender interior face that catches a fried egg's yolk or holds a fold of soft scramble. The egg is cooked to stay moist: fried with the yolk set enough to handle but loose enough to seep into the crumb, or scrambled soft and sized to the biscuit so it does not push out the sides. Salt and pepper and sometimes a touch of butter or hot sauce are the only seasoning, because the sandwich is deliberately plain and the biscuit's richness is doing what a condiment would do elsewhere. This is fast morning food, assembled while the biscuits are still warm and eaten one-handed, which is why the biscuit has to hold its structure without going dry.
There is not far to vary before it becomes a different sandwich, which is the nature of a build this spare. Adding cheese, or bacon, sausage, or country ham, turns it into one of the named meat-and-biscuit sandwiches; a smear of jam or a drizzle of honey pushes it toward the sweet side of the biscuit's range. The broader breakfast family runs from the bodega kaiser roll to the bagel to the New Jersey pork roll. Each of those is a codified build with its own following and deserves its own article rather than being crowded in here.