Peel the potato and cut into smaller pieces and steam until they are fork tender and can be easily mashed. Transfer the purple sweet potato, coconut cream, and food coloring in a blender and blend until smooth. It will be thick, but smooth. I get a better result when I do this part first before combining them into the batter. Set aside.
In the same steamer, steam the grated coconut with 1/4 tsp of salt for 10 minutes. Set aside
Brush the puteri ayu mould with some cooking oil on the base and the side of the mould. If you don't have one, you can use small muffin cups. Portion out the steamed grated coconut into the muffin cups. Make sure to PRESS the coconut down firmly with your fingers on the base of the cups so when you invert the cake the grated coconut won't come "loose"
Place the eggs and sugar in a mixing bowl. I used a stand mixer with whisk attachment. Beat on medium speed for 5 minutes and then increase to high speed and beat for another 10-15 minutes or until they have reached ribbon stage. When you lift the whisk up, the batter will drop down leaving a trail that remains visible for 10 seconds or so before dissolving back into the batter. The volume will triple up too. Reduce the speed to medium and in mashed purple yam, coconut milk mixture and stir until all mixed in.
Add few drops of purple food gel if using. Please note that without food gel/coloring or extract, the natural purple color may change into greenish/bluish after baking and this is normal. Reduce the speed to low and add vanilla, salt, and all-purpose flour. The idea is just to mix in the flour. You don't want to overbeat the flour. Turn off the mixer and use a spatula to fold in the rest of the flour until no more pockets of flour are visible
Portion out the batter into the muffin cups you have prepared with coconut earlier, about 3/4 cup full. Steam for 15 minutes over medium heat
Remove from the steamer and wait for 5 minutes before removing from the cups. If necessary, run a knife at the side of the cup to loosen the cake. They shouldn't be very sticky or difficult to remove. Invert into a serving platter. The coconut portion should be on top as shown in the photos. Serve warm or room temperature
You can store the rest in the refrigerator in an air-tight container up to 3 days. Just reheat in the microwave for few seconds (I'm not sure because we don't use microwave) or in the steamer for 5 minutes
You don't have to use a purple food coloring. Without food coloring, the color will naturally be dark purple after steaming
Kuih Puteri Ayu Ubi Ungu / Putu Ayu (Purple Sweet Potato Puteri Ayu) https://whattocooktoday.com/putu-ayu.html