Whisk egg yolks with milk or buttermilk and melted butter. Gradually add this mixture to the dry ingredients mixing with spatula. Do not beat. The batter should still have some small lumps of flour which will disappear as the waffles bake. Gently fold in beaten egg whites.
Most waffle irons have a ready indicator light.
To prevent batter from sticking to grids, wait until the waffle iron is at the proper temperature before adding batter. Batter will be thick so it won't actually pour, but using a spatula, push off or spoon batter onto the hot waffle iron. Spread an even layer across the lower griddle, level off with a table knife. Batter should just barely hide the upright waffle grids. Close the cover.