Soak snow fungus in a bowl of hot water until it is puffed up and turn a whiter shade, then carefully drain soaking water. Using a pair of kitchen scissors, trim and discard the dark yellow hard part on the centre underside of the fungus. Cut the rest of the fungus to smaller pieces and set aside. In a soup pot, add water, fungus, pandan, longan and red dates. Bring to a boil and then simmer (with lid partially closed) for 20 minutes. Add gingko nuts and continue simmering for 10 minutes. Add rock sugar to taste and stir through until the sugar is fully dissolved. Discard pandan leaves. Serve warm or chilled.