Pre-heat oven to 350 degrees. Generously grease an 8X8 baking pan with melted butter or cooking spray. Or line it with aluminum foil.
Mix flour, baking soda, corn starch, and salt in a medium sized bowl.
In a large bowl, mix butter, brown sugar and vanilla. Add egg (make sure your butter isn't too hot still so it doesn't start to cook the egg) and stir until combined.
Add flour mixture to egg and sugar mixture and stir until just combined.
Fold in white chocolate chips.
Add to baking pan. It will be a very thin layer. You may think you don't have a enough batter - you do! Just spread it very thin.
Bake for 24-30 minutes until edges begin to slightly brown.
Cool, cut and store in an air tight container up to a week.