Prepare a 8x8 baking dish with parchment paper. Preheat the oven to 350 degrees Fahrenheit.
In a mixing bowl add the melted butter to the white and brown sugar. Whisk together the two ingredients. They will stay separated for a while when mixing, so don’t stop until they are completely combined, between 1 and 2 minutes.
Then add the egg and vanilla extract. Whisk again until combined.
In a separate bowl, whisk together the flour, baking powder and salt.
Pour the flour mixture into the melted butter mixture and toss in the raspberries as well.
Gently fold these two together until almost completely combined.
Then add the white chocolate chips, folding all the ingredients once more until evenly distributed and no flour streaks remain.
Pour this thick batter into the prepared baking pan and spread evenly. Top with extra raspberries and white chocolate chips, to ensure the pops of red will be shown throughout.
Bake in the oven for 30-35 minutes or until a toothpick inserted comes clean.
Remove from the oven and let cool for at least 15 minutes before removing the parchment and blondies from the pan.
Optional: melt some white chocolate chips in a microwave-safe bowl - for 15-20 seconds at a time until melted. Do not burn! Pour melted white chocolate into Ziploc with snipped corner or into an icing bag with tiny tip. Drizzle melted chocolate in a pattern across the tops of blondies.
Cut into even squares - 9 or 12.