Preheat oven to 350 degrees F.
Line with parchment paper and grease a 9X9 inch pan.
In a medium bowl, whisk together all purpose flour, salt, baking powder and corn starch, set aside.
In another medium bowl whisk together browned butter (see notes), brown sugar and white sugar until smooth. Add in eggs and vanilla extract, whisk once more until smooth.
With a rubber spatula gently fold in the flour mixture to the butter/sugar mixture in two increments until well incorporated. Stir in white chocolate chips, and 1/4 cup of sprinkles. Transfer batter into baking pan and into a preheated oven.
Bake blondies for 10 minutes. Remove from oven and sprinkle top with an even layer of remaining sprinkles. Continue to bake for 10-15 minutes or until a toothpick inserted comes out clean.
Cool for 20-30 minutes before removing from the pan and cutting blondies.