Preheat your oven to 350F. Line an 8x8 inch baking pan with parchment paper and lightly grease the sides.
In a large bowl, whisk together the melted butter and brown sugar until smooth and combined. Add the egg, egg yolk, and vanilla extract. Whisk vigorously until the mixture is thick, smooth, and slightly glossy.
Add the flour, baking powder, and salt. Fold with a spatula until just combined with no dry pockets remaining. Fold in the white chocolate chips.
Pour the batter into the prepared pan and spread it evenly. Scatter the fresh raspberries across the top, pressing them very gently into the surface of the batter.
Bake for 28 to 32 minutes, until the top is golden and set and a toothpick inserted in the center comes out with just a few moist crumbs. The raspberries will burst and create beautiful jammy pockets throughout.
Let the blondies cool completely in the pan before slicing. For the cleanest cuts, refrigerate for 30 minutes first. The blondies will be fudgy, chewy, and loaded with melty white chocolate and tart raspberry in every bite.