Preheat oven to 350 degrees F
In a large bowl or stand mixer, combine the melted butter and brown sugar and mix with a wooden spoon, fork or paddle attachment for 1 minute until combined. Add the vanilla and eggs, making sure to scrape down the sides of the bowl, and mix until fully incorporated.
Add the dry ingredients into the bowl/stand mixer and slowly mix until just combined. The batter will be a bit stiff, but that's normal. Fold in almost all of the white chocolate chips, leaving a few for sprinkling on top.
Spray a 9x9 baking pan with baking spray and line it with parchment paper. Spoon the batter into the prepared baking pan and sprinkle with the remaining white chocolate chips. Sprinkle the blueberries on the top of the blondies and press down ever so slightly so they set into the dough. Transfer the baking pan into the oven and bake for 35-40 minutes, use a toothpick or knife to insert into the center and make sure they are done. Once the bars have baked, remove them from the oven and let cool for at least 2 hours before cutting and serving.