Remember, the thicker the bread, the smaller the hole needed.
Use a glass (or biscuit cutter if you have one) to cut a nice hole in the center of the bread
Butter one side of the bread and place the dry side down on a buttered cast-iron skillet.
Crack the egg in the hole and sprinkle with a dash of salt and a fair amount of freshly ground black pepper.
Let it cook up for a few minutes.
When the egg starts to set, you can (a)flip it over and continue cooking, OR you can put the entire pan in the broiler for a minute or two (I used this method).