Combine and mix milk, egg yolks and vanilla in a medium bowl.
Beat egg whites until stiff in a large bowl.
Add milk and egg yolk mixture to dry ingredients. Beat with electric mixer at high speed just enough to moisten dry ingredients.
Stir in slightly cooled butter. Fold in egg whites, leaving little fluffs of them showing in batter.
Pour batter onto center of heated waffle iron. Pour in center of griddle until it spreads to about 1" from edges and cook until browned and done. My iron takes about 6 minutes but I know they will vary.