2. Wash the blueberries, drain the water, put them in a pot, add a little water and rock sugar, and boil them over high fire.

3. Break blueberries with a cooking stick.

4. Squeeze in half a cup of lemon juice and cook for another three minutes on low heat.

5. Scoop out the floating foam, filter it into a cup and put it in the refrigerator for refrigeration.