Preheat your oven to 350°F (175°C) and prepare an 8-inch square baking pan with cooking spray and parchment paper.

In a small bowl, whisk together the mochiko sweet rice flour, baking powder, and kosher salt until well blended.

In a medium bowl, whisk together the melted butter and granulated sugar until smooth, then add the eggs, followed by ube halaya jam, ube extract, and coconut milk, mixing well.

Gradually combine the dry ingredient mixture into the wet mixture, stirring gently until just blended without overmixing.

Pour the batter into the prepared pan and smooth the surface, then bake for 48-50 minutes until a toothpick comes out with a few crumbs.

Allow the cake to cool in the pan for about 10 minutes before transferring to a wire rack to cool completely before cutting.