Line a metal 9”x 9” baking dish with parchment paper and spray with cooking spray. Preheat the oven to 350 degrees F.

In a small bowl, whisk together the flour, cornstarch, baking powder, and Kosher salt. Set aside.

Add the brown sugar to a medium sized bowl and pour in the melted butter. Whisk until well combined and glossy, about 30 seconds.

Add the eggs and the vanilla to the butter mixture and whisk very well for about 60 seconds until smooth and shiny. This will help dissolve the sugar and give the top of the blondies a crisp crust.

Add the dry ingredients to the wet ingredients and fold gently until almost fully combined, but streaks of flour are still showing.

Pour in ¾ cup of white chocolate chips. Gently fold until the chips are evenly distributed and no streaks of flour remain.

Scoop the batter into the prepared baking dish and gently spread the blondie dough out to the edges. Sprinkle the remaining ¼ cup of white chocolate chips evenly over the top. Press lightly into the batter.

Bake at 350 degrees F for 25-30 minutes until a toothpick inserted comes out with fudgy crumbs -not clean- and the top is puffed and shiny. Do not overbake.

Let the blondies cool for 2 hours before slicing, the center should be gooey and fudgy but set.