Set the oven to 350°F (175°C). Prepare an 8x8-inch baking pan by lining it with parchment paper or lightly greasing it with butter or cooking spray for easy removal.

In a microwave-safe bowl, melt 6 tbsp unsalted butter and 2/3 cup white chocolate chips by microwaving in 30-second intervals, stirring in between, until smooth and fully melted. Let it cool slightly.

In a large bowl, whisk 3 eggs, 1/4 cup brown sugar, and 3/4 cup white sugar with an electric mixer on medium speed for 5-8 minutes, until the mixture thickens and turns a pale purple color.

Gradually add the melted butter and white chocolate mixture to the egg mixture, stirring until smooth and glossy.

Gently fold in 3/4 cup all-purpose flour using a rubber spatula, mixing just until combined. Be careful not to overmix the batter.

Stir in 3/4 tbsp ube extract to achieve a vibrant purple hue. Optionally, fold in 1/3 cup of espresso chips for a rich flavor.

Pour the batter into the prepared pan and spread it evenly. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean or with just a few moist crumbs.

Let the brownies cool in the pan for approximately 10 minutes before transferring them to a wire rack to cool completely. Once fully cooled, cut into squares and enjoy the fudgy texture.