Preheat your oven to 350°F (175°C). Spread the white chocolate evenly on a baking sheet lined with parchment paper. Bake for about 10-15 minutes, stirring every 5 minutes, until the chocolate is golden brown and has a nutty aroma. Keep a close eye on it to prevent burning.
In a medium saucepan, melt the unsalted butter and finely chopped dark chocolate over low heat. Stir continuously until melted and smooth. Remove from heat and let it cool slightly.
In a large mixing bowl, whisk together the eggs and granulated sugar until well combined and slightly frothy. Add the melted chocolate mixture, vanilla extract, and buttermilk, mixing until incorporated.
In another bowl, sift together the all-purpose flour, cocoa powder, salt, and baking powder. Gently fold the dry ingredients into the wet mixture until just combined. Be careful not to overmix!
Once the white chocolate is caramelized, let it cool slightly. Reserve a few tablespoons for topping, and fold the rest into the brownie batter gently, creating a swirl effect.
Pour the brownie batter into the prepared baking pan, smoothing the top with a spatula. Drizzle the reserved caramelized white chocolate on top and use a knife to create a marbled effect. Bake for 25-30 minutes or until a toothpick inserted in the center comes out with a few moist crumbs.
Remove the brownies from the oven and let them cool in the pan for at least 15 minutes. Lift them out using the parchment paper and transfer to a wire rack to cool completely before slicing into squares.
