In a saucepan, melt the granulated sugar over medium heat until it turns golden brown.

Quickly pour the melted caramel into the bottom of the prepared cake pan and swirl it around.

In a blender, combine the ube halaya, evaporated milk, condensed milk, and eggs. Blend until smooth.

Carefully pour the flan mixture over the hardened caramel in the cake pan.

In a mixing bowl, whisk together the all-purpose flour, baking powder, and salt.

In another bowl, combine the ube halaya, vegetable oil, milk, and vanilla extract.

Gradually add the dry ingredients to the wet mixture, stirring until just combined.

Gently pour the cake batter over the flan mixture in the pan.

Place the cake pan in a larger baking dish filled with water and bake at 350°F (175°C) for about 60 minutes.

Once baked, let the cake cool at room temperature, then refrigerate for at least 4 hours or overnight.