Preheat your oven to 325°F. Line a 9x9-inch baking pan with aluminum foil or parchment paper, leaving overhang on two sides for easy lifting.

In a large microwave-safe bowl, combine 1 1/4 cups of white chocolate chips and the cubed butter. Microwave in 30-second bursts, stirring after each, until completely melted and smooth.

Using a sturdy wooden spoon, stir in both sugars, then the eggs and vanilla extract, mixing well. Add the flour and salt, stirring just until no streaks of flour remain. Fold in the remaining 1/2 cup white chocolate chips.

Pour the batter into the prepared pan and spread evenly. Bake for 20-24 minutes, until the edges are set and the center still looks slightly underdone. For fudgy brownies, an internal temperature of 180-190°F is ideal. Let cool completely in the pan on a wire rack.

In a microwave-safe bowl, warm the heavy cream in 30-second increments until hot but not boiling. Add the white chocolate chips, ensuring they are fully submerged, and let sit for 3 minutes. Stir gently until the mixture is completely smooth and glossy.

Pour the ganache over the cooled brownies and spread into an even layer. Refrigerate for at least 30 minutes, or until the ganache is firm. For clean slices, chill for 1 hour before cutting. Store leftovers in the refrigerator, covered.