Cut a circle in the middle of the bread. I personally use a cup to get the circle shape. You can use a bowl or something round too.

Heat butter in the pan

Put the slice of bread with a hole in the pan.

Crack an egg into the hole on the bread.

Leave it in the pan till egg is cooked. You can also take it out half cooked, if you prefer it that way.

Take the slice of bread out from the pan.

I would suggest not to waste the circle piece of bread that was cut out. So, perhaps you would like to add some mayonnaise or some other sauce on it and use it as a saucer which could be eaten after that.