Preheat your oven to 350°F and prepare an 8x8 baking dish by lining it with parchment paper.

In a mixing bowl, combine the melted butter with the granulated and brown sugars, whisking for about 1 to 2 minutes until fully blended.

Add the egg and vanilla extract, whisking until well combined with the butter mixture.

Gently incorporate the flour, baking powder, and salt into the mixture until just combined.

Carefully fold in the frozen raspberries.

Next, stir in the white chocolate chips, ensuring even distribution without leaving any flour streaks.

Pour the thick batter into the prepared pan and spread it evenly.

For an appealing finish, sprinkle some additional raspberries and white chocolate chips on top.

Bake in the preheated oven for about 30 to 35 minutes, or until a toothpick inserted into the center comes out clean.

Allow the blondies to cool for at least 15 minutes before lifting them from the pan.

Cut into squares and, if desired, drizzle with melted white chocolate before serving.