Heat the butter in a nonstick skillet over medium heat until melted and lightly foaming.
Carefully break the eggs into the skillet.
Cook the eggs until the whites are set on top and the yolks are still runny, about 2 minutes.
Use a spatula to flip the eggs and let cook for another 5 to 10 seconds. Transfer to a plate and season with kosher salt and black pepper. Serve with toasted bread and sliced avocado.