2. Wash the yam, peel it, cut it into pieces, put it in a plate, pour the water into a steamer and steam it for 20 minutes on high fire until the yam becomes soft. Steam the yam until there is no hard core. You can poke it with chopsticks and take it out of the pot. Then put it in a bowl and press it into fine mud with a spoon. Add light milk and salt and mix well.
3. Pour water into the pot and add blueberry sauce and rock sugar. After the fire boils, turn to low heat and continue to cook until the blueberry sauce and water become sticky, then pour out and cool.
4. Put the piping mouth into the piping bag, and then put the yam mud into the piping bag. Finally, squeeze into the container and pour with blueberry sauce.