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 no lumps remain.

In a medium bowl, blend the melted butter and granulated sugar, then beat in the eggs one at a time before adding ube halaya jam, ube extract, and coconut milk.

Gradually combine the dry mixture with the wet ingredients, stirring gently until just incorporated.

Pour the batter into the prepared pan and bake for 48 to 50 minutes, or until a skewer comes out with a few moist crumbs.

Allow the cake to cool completely in the pan on a wire rack before slicing and serving.