Preheat a non-stick frying pan over medium heat.

Add butter to the pan and let it melt.

Crack the egg into the pan and let it cook until the white is set and the yolk is still runny.

Season the egg with salt and black pepper to taste.

Toast the bap in a toaster or under a grill until lightly browned.

Place the cooked egg on the bottom half of the bap and cover with the top half of the bap.

Serve immediately.