Add butter to a medium sauce pan. Completely melt over medium heat, then continue to stir over medium heat 4-6 minutes longer until butter reaches a deep golden color.
Add brown sugar, vanilla, and egg to sauce span and whisk until smooth.
Add flour, baking powder, baking soda, and salt to a medium bowl and whisk to combine. Add ingredients from sauce pan and stir until combined.
Spread batter in a 9 inch cast iron skillet OR 2 6 inch cast iron skillets. (You can use other sizes, only fill them half-way full because the blondie will rise slightly and you don't want it to spill over.)
Sprinkle white chocolate chips over blondie batter. Bake at 375 12-15 minutes or until an inserted toothpick comes out mostly clean. (You may need to increase baking time if you are using a large skillet)
Allow to cool slightly, then (optional) top with ice cream and caramel sauce (or butterscotch sauce) and serve. You may also serve the blondie at room temperature with or without ice cream.
Notes
Pro tip: top it off with vanilla ice cream, caramel sauce, and sea salt flakes!