Coat a waffle iron with cooking spray, and preheat.

Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, baking powder, and salt in a large bowl. Place milk, butter, vanilla, and egg yolk in a bowl; stir with a whisk. Add to flour mixture, stirring until blended. Beat egg white and sugar with a mixer at high speed until stiff peaks form. Fold into flour mixture. Fold in mini chocolate chips.

Spoon about ½ cup batter onto hot waffle iron, spreading batter to edges. Cook 3 to 5 minutes or until done; repeat procedure with remaining batter.