01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper, allowing overhang for easy removal.
02 - Whisk melted butter, sugar, and ube halaya in a large bowl until smooth and fully combined.
03 - Beat in eggs and vanilla extract until completely incorporated into the mixture.
04 - Sift flour, salt, and baking powder into a separate bowl.
05 - Gently fold dry ingredients into ube mixture, mixing just until combined. Avoid overmixing.
06 - Melt chocolate with butter in microwave-safe bowl in 30-second intervals, stirring until smooth.
07 - Spread ube batter evenly in prepared pan. Dollop melted chocolate on surface, then swirl with skewer or knife to create marble pattern.
08 - Bake 32-36 minutes until toothpick inserted in center comes out with moist crumbs.
09 - Cool completely in pan before lifting out and cutting into squares.