Pre-heat oven to 350 degrees. Coat 8x8 pan with non-stick spray.
Whisk sugars, egg whites, vanilla, and salt into melted butter until well combined. Let mixture rest for 3 minutes, whisk again. Repeat rest/whisk cycle a total of three times. This helps the sugars dissolve and make the blondies extra chewy.
Stir in flour, baking soda, and cranberries (or chocolate chips, nuts, ect). Spread mixture into prepared pan. Bake for 15-20 minutes until light brown and set. Let cool, slice, and eat!