1. The yam is peeled, washed and cut into pieces, soaked in clean water to prevent oxidation.
2. Wash the lotus seeds and put them in a pot, add enough water.
3. Bring to a boil on high heat, cover and turn to low heat and simmer for 30 minutes.
4. Open the lid and add the yam, turn to medium heat and cook for about 10 minutes.
5. Add rock sugar and cook until the rock sugar melts, then turn off the heat.
6. Put it into a bowl and eat.