3/4 c. all-purpose flour
1/2 c. cornstarch
1/2 tsp. salt
1/2 tsp. baking powder
1/4 tsp. baking soda
3/4 c. buttermilk
1/4 c. milk
6 tbsp. vegetable oil
1 egg, separated
1 tbsp. sugar
1/2 tsp. vanilla extract

Heat oven to 200°F. Mix flour, cornstarch, salt, baking powder and baking soda in a medium bowl. Measure buttermilk, milk and vegetable oil in a 2-cup measuring cup; mix in yolk and set aside.

Beat egg white in a small bowl to almost soft peaks. Sprinkle in sugar and continue to beat until white and glossy. Beat in vanilla extract. Pour wet ingredients into dry ingredients and whisk until just mixed. Fold in egg white until just incorporated. Add batter to hot waffle iron and cook until crisp and brown. Set waffle directly on rack in preheated oven to keep it warm and crisp at least 5 and up to 20 minutes.