Lightly grease and flour the inner pot of your rice cooker.

In a large bowl, whisk together the egg yolks, half of the granulated sugar (1/4 cup), milk, neutral oil, and ube extract until well combined and smooth.

Sift the cake flour and baking powder into the wet mixture. Gently fold until just combined, being careful not to overmix. The batter will be thick.

In a separate, clean bowl, beat the egg whites with cream of tartar until soft peaks form. Gradually add the remaining half of the granulated sugar (1/4 cup), beating until stiff, glossy peaks form.

Gently fold about one-third of the meringue into the ube batter to lighten it. Then, carefully fold in the remaining meringue in two additions, taking care not to deflate the mixture. Mix until no streaks of egg white remain.

Pour the batter into the prepared rice cooker pot. Gently tap the pot on the counter a few times to release any large air bubbles.

Place the pot into the rice cooker and set it to the 'White Rice' or 'Cake' function. If your rice cooker automatically switches to 'Keep Warm,' you may need to run the cooking cycle 2-3 times until the cake is fully cooked (about 45-60 minutes total). Do not lift the lid during cooking.

To check for doneness, insert a wooden skewer or toothpick into the center of the cake. If it comes out clean, the cake is ready.

Once cooked, turn off the rice cooker and let the cake cool in the pot for about 10-15 minutes. This helps it firm up and prevents it from sticking.

Carefully invert the pot onto a wire rack to release the cake. Allow it to cool completely before slicing and serving. Enjoy your vibrant Ube Rice Cooker Sponge Cake!