Preheat oven to 350° F/180° C.
Combine flour, cornstarch, baking powder and salt in a medium bowl.
In the Whip 'N Mix Chef, combine butter and brown sugar, cover and mix on gear II until combined.
Add eggs and vanilla extract and mix.
Staying on gear II, add ⅔ cup of the flour mixture and mix just until combined. Repeat with another ⅔ cup of flour.
Add white chocolate chips and pecans to the remaining flour then fold into batter until you have a consistent mixture.
Spread batter evenly in the Ultra Pro 2-Qt./2 L Casserole Pan.
Bake for 25–30 min. Allow to cool completely before unmolding.