Heat electric griddle to 375 degrees. Whisk flour, cornmeal, baking powder, baking soda, salt, and sugar in a bowl. Add egg yolks, buttermilk, and 4 tablespoons butter; whisk to combine. Batter should have small to medium lumps; fold in egg white.
Heat oven to 175 degrees. Test griddle by sprinkling a few drops of water on it. If water bounces and
spatters off griddle, it is hot enough. Using a pastry brush, brush remaining 1/2 teaspoon of butter onto griddle. Wipe off excess.
Using a 2-ounce ladle (about 1/4 cup) pour batter in pools 2 inches apart. When pancakes bubble on top and are slightly dry around edges, about 2 1/2 minutes, flip. Cook until golden on bottom, about 1 1/2 minutes.
Place on plate in preheated oven until ready to serve.
I've got my own recipe for these kind of pancakes. In the UK these are know as drop scones or scotch pancakes, but whenever I served them to anyone from the USA, they all commented that they were exactly like American pancakes. My recipe came from The Sunday Times Cookbook (I think this is the title, but sadly my book didn't make the move to the UAE!) there's not enough characters to fully give you the recipe...sorry! I've not tried adding melted butter may try it one day!