Preheat your oven to 350°F (175°C) and line an 8x8 inch baking pan with parchment paper.

In a microwave-safe bowl, melt the butter and semi-sweet chocolate together in 30-second intervals, stirring until completely smooth.

Whisk the sugar, eggs, and vanilla extract into the melted chocolate mixture until the batter looks glossy.

Gently fold in the flour, cocoa powder, and salt until just combined; be careful not to overmix.

Pour the brownie batter into the prepared baking pan, spreading it out evenly.

In a separate small bowl, melt the white chocolate chips carefully in the microwave.

Lightly mash the fresh raspberries with a fork to break them up.

Drop spoonfuls of the melted white chocolate and the mashed raspberries randomly over the top of the brownie batter.

Use a butter knife or toothpick to gently swirl the toppings into the batter to create a marbled effect.

Bake for 30 to 35 minutes, or until a toothpick inserted into the center comes out with moist crumbs.

Allow the brownies to cool completely in the pan before lifting them out and slicing into squares.