1Mix masarepa and salt. Add hot water and melted butter. Cover with plastic wrap and let sit 10 minutes.
2Reserve 2 tablespoons of dough. Shape rest of dough into 4 balls.
3Place one ball between 2 pieces of plastic wrap and press with a heavy skillet until 3" in diameter and 1/3" thick.
4Heat oil in skillet until small piece of dough sizzles. Fry arepas until golden on each side, 2-3 minutes. Place on paper towel.
5When cool enough to handle, partially split arepas. Break egg into small bowl, then pour into arepas. Seal split area with extra dough.
6Fry arepas about 3 minutes per side - less, if you like runny eggs, more if you like firm eggs. Season with salt and pepper.