01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper, leaving an overhang for easy removal.
02 - Whisk together melted butter, sugar, and ube halaya in a large bowl until smooth and fully combined.
03 - Beat in eggs and vanilla extract, whisking until the mixture is completely incorporated and slightly thickened.
04 - Sift flour, salt, and baking powder into a separate bowl, breaking up any lumps.
05 - Gently fold the dry ingredients into the ube mixture using a spatula, mixing just until no dry streaks remain.
06 - Melt chocolate with 2 tablespoons butter in a microwave-safe bowl, heating in 30-second intervals and stirring until smooth.
07 - Spread ube batter evenly in prepared pan. Dollop melted chocolate on top in several spots, then swirl with a knife or skewer to marble.
08 - Bake for 32–36 minutes until a toothpick inserted into the center emerges with a few moist crumbs.
09 - Cool completely in the pan before lifting out using the parchment overhang and cutting into squares.