In an 8-inch omelet pan or skillet over medium-high heat, add butter or cooking oil when pan is hot enough to sizzle a drop of water.
Break egg into pan. Immediately reduce heat to low.
Cook eggs slowly until whites are completely set and yolks begin to thicken but are not hard, covering tightly with lid (adding 1 teaspoon water after edges turn white for steambasted, if desired), spooning butter over edges to baste or turning eggs to cook both sides.
For over easy or over hard, gently lift eggs with a pancake turner and flip upside down into pan to cook second side.