Preheat your oven to 350°F (175°C).
Line an 8x8-inch baking pan with aluminum foil, leaving some overhang on the sides for easy removal. Spray the foil with non-stick cooking spray and set aside.
In a medium microwave-safe bowl, combine the butter and white chocolate.
Microwave in 20-second bursts, stirring after each interval, until both are fully melted and smooth.
Let the mixture cool for 5 minutes.
Whisk the granulated sugar into the melted butter and white chocolate mixture until well combined.
Add the vanilla extract, eggs, and salt, and whisk until the mixture is smooth and fully incorporated.
Gently fold in the all-purpose flour using a spatula until just combined. Be careful not to overmix.
Pour or spoon the batter into the prepared baking pan, spreading it evenly.
Bake for 20–24 minutes, or until the top is set and the edges start to pull away from the pan. To test for doneness, insert a toothpick into the center—it should come out with a few moist crumbs or clean.
Let the brownies cool completely in the pan.
Once cooled, lift them out of the pan using the aluminum foil overhang. Carefully peel back the foil and cut the brownies into 9 or 12 squares.
In a small microwave-safe bowl, melt the white chocolate chips in 20-second bursts, stirring between each interval, until smooth. Drizzle the melted white chocolate over the brownies.
Repeat the process with the semi-sweet chocolate chips, drizzling them over the brownies for a decorative finish.
Allow the chocolate drizzle to set slightly before serving. Enjoy your delicious, fudgy white chocolate brownies!