Pour water at 1/4 level in a large pot.

Steam 200g of purple sweet potato until it's soft.
Let it cool so that you can handle them without hurting your fingers.
Then cut it in half.
Scoop out most of purple sweet potato flesh and put it into a large bowl.

Give 150g of grated coconut and 1/2 teaspoon of salt a good shake.

Meanwhile place the coconut in a small pot under the same large pot.
Steam the coconut for around 5 minutes to prevent it from turning sour.

Crush 100g of gula melaka and set aside.

Mix the mashed purple sweet potatoes, 60g of glutinous rice flour and 40g of tapioca flour together.
Knead it well.
Add 8 tablespoons of warm water each at a time to smoothen the dough.
Until you can feel that the texture is smooth and the dough no longer sticks to your fingers.
Cover the dough and set aside for about 15 minutes.

When the dough is ready, you start 1/2 boiling water of the large pot.
Make the balls.
Flatten each ball.
The gula melaka is stuffed into each center of the balls.
Be gentle when you pinch the edges of the balls to secure the filling.
Roll the balls again.

Don't leave the rolled balls to stand as the gula melaka filling will ooze out.
Put the balls into the pot of boiling water and give them a few stirs during cooking.

Once the balls float to the surface, remove them with a slotted spoon and shake off the excess water.
Roll the balls in the steamed grated coconut.
Serve and finish ondeh-ondeh on the same day.