Preheat the oven to 350℉/180℃. Grease an 8×8 inch square pan. For easy removal of the blondies, place parchment paper on the bottom and 2 sides of the pan. Grease again and then set side.
In a large bowl, whisk the cooled and melted butter and brown sugar. Add in bananas and continue whisking.
1 cup butter, 1 cup light brown sugar, 1 cup mashed bananas
Add in eggs and vanilla and keep on whisking.
2 eggs, 1 tbsp vanilla
Add in flour and salt. Slowly mix in using a spatula until no flour streaks appear. Do not overmix!
2 cups all-purpose flour, 1/4 tsp salt
Toss in white chocolate and mix in a few times.
1/2 cup white chocolate
Transfer into the prepared pan and spread out evenly. Add more white chocolate on top if desired. Bake the bars for 25-30 minutes. A toothpick inserted should come out with a few moist crumbs on it. If it is wet, it isn't ready yet. Continue to bake at 5 minute intervals until the edges are set.
Remove the pan from the oven and cool the bars on a wire rack before cutting into squares.