In a nonstick or cast iron pan, melt the butter over medium-low heat for about 2 minutes.
Crack the egg on a flat surface and gently open it over the pan, ensuring the yolk doesn't break. Let the egg cook for 2-3 minutes until the whites are mostly set.
Using a thin, wide spatula, slide it gently under the egg, making sure to get under the yolk. In one smooth motion, quickly flip the egg over. Cook for an additional 1-2 minutes, until the yolk is jammy and slightly runny.
Gently slide the spatula under the egg, lift it from the pan, and carefully place it on a plate to serve. Season with salt and pepper.