1. Peel and cut the sweet potato into small pieces.
2. Cook it until soft and then drain the cooking water.
3. Transfer the sweet potato pieces to a bowl and add 1 cup of water, sugar, vanilla and agar agar.
4. Blend very well until completely integrated.
5. Pour the mixture into a saucepan and cook over medium heat for 5 minutes.
6. Remove from heat and let stand at room temperature.
7. Refrigerate for 3 hours.