Boil the eggs until they are well done and shell them. Blanch the peanuts and dates for 5 minutes, so as to remove their raw smell. Finely slice the ginger. Put the preserved plums, ginger, sugar crystals, soy sauce and vinegar into a pot of water to make a sauce. Boil the eggs, dates and peanuts in the sauce for 20 minutes. Turn off the heat and leave the eggs, dates and peanuts immersed in the sauce of 2 hours, thus they can sufficiently absorb the flavourings. Boil the stew again with strong heat, until the sauce thickens.