Preheat your oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper and set aside.
In a large mixing bowl, whisk together the melted butter and cocoa powder until smooth and glossy.
Add the granulated sugar and brown sugar, whisking until fully combined.
Whisk in the eggs one at a time, then stir in the vanilla extract.
Gently fold in the flour and salt just until no dry streaks remain. Do not overmix.
Stir in most of the white chocolate chips, reserving a small handful for the top.
Pour the brownie batter into the prepared pan and spread evenly.
Spoon small dollops of raspberry preserves across the surface of the batter.
Use a knife or skewer to gently swirl the raspberry preserves into the batter, creating a marbled effect.
Sprinkle the remaining white chocolate chips over the top.
Bake for 30–35 minutes, or until the edges are set and the center is slightly soft.
Allow brownies to cool completely in the pan before slicing and serving.