In a medium bowl, combine melted butter and Splenda Brown Sugar Blend . Stir until sweetener is completely dissolved. Stir in applesauce. Whisk in eggs and egg yolk. Stir in vanilla extract.
In a separate bowl, stir together dry ingredients: flour, cornstarch, salt, and baking powder. Add the dry ingredients to the wet, and stir until everything is incorporated. Stir in white chips.
Pour into a 9×13 inch pan lined with parchment paper or sprayed with nonstick cooking spray. Bake for 30 minutes, or until a toothpick comes out mostly clean.