Butter the ramekins and set aside.
While the potatoes are still warm, add the salt, softened butter, milk and two eggs, and mix well.
Lightly press some potatoes into the bottom of each ramekin, trying to keep the layer level.
Chop the bacon into bite-sized pieces, then add one quarter of the bacon to each ramekin, then add another layer of potatoes.
With a fork, make a large well in the center of the top layer of potatoes, without disturbing the bacon, pressing them toward the sides of the ramekins.
If baking these immediately, add an egg to the well, and sprinkle with salt (and pepper, if desired), and spray with a touch of olive oil. (If making ahead of time to bake later, cover and refrigerate for up to 24 hours, and skip the next step; bring to room temperature before baking).
Place the ramekins on a baking tray and put in the center of the oven for about 18 minutes, or until the egg whites are cooked, but yolks are still a little runny (eggs will continue to cook once removed from the oven).
Let stand for a few minutes before serving, then enjoy with a cup of your favorite hot beverage!