Preheat your oven to 180°C (355°F) and prepare an 8-inch square baking tin by lining it with parchment paper, ensuring the edges extend over the sides for easy removal.

In a heatproof bowl, combine the butter and white chocolate, and gently melt them using a double boiler or microwave. Stir frequently until you achieve a smooth, glossy mixture. Set aside to cool slightly.

In a large mixing bowl, whisk together the ube halaya jam, eggs, ube extract, sugar, and salt. Beat until the mixture is smooth and well-combined, creating a rich and vibrant base.

Gradually pour the cooled butter and chocolate mixture into the ube mixture, whisking constantly to incorporate the two without curdling. Ensure the batter becomes silky and uniform.

Sift the all-purpose flour over the wet ingredients and gently fold the mixture until just combined. Avoid overmixing to maintain a tender crumb.

Scatter the white chocolate chunks into the batter, folding gently to distribute them evenly.

Pour the batter into the prepared baking pan, spreading it evenly into the corners with a spatula. Bake for approximately 30 minutes, or until a toothpick inserted into the center emerges with a few moist crumbs clinging to it.

Allow the brownies to cool completely in the pan before dusting with purple sweet potato powder, if desired, for a pop of color and flavor.

In a small bowl, mix the powdered sugar, milk, and vanilla extract until smooth and free of lumps. If a vivid purple hue is preferred, add a drop or two of purple food coloring and stir until evenly blended. Adjust the consistency by adding more milk for a thinner drizzle or more powdered sugar for a thicker one.

Drizzle the icing artfully over the cooled brownies, allowing it to cascade naturally for a decorative finish. Slice and serve.