Preheat and lightly grease a large skillet or griddle. (I like to use my 2-burner cast iron griddle for pancakes.) Mix the flour, salt, baking soda, and sugar together in a bowl. Add the egg, milk mixture, and butter; stir together lightly, but keep it lumpy. Let sit for 5 minutes. The batter should look thick and a bit bubbly. Drop 1/3 cup of the batter onto the cooking surface, spreading lightly with the bottom of the cup. Cook until lightly-browned on each side, 2 to 4 minutes per side.