1. Mix the plain flour, thick sugar syrup, lye water and oil into a dough.
2. Chop up the lotus seed paste into small pieces and then put the salted egg yolk into small cube of lotus seed paste.
3. Roll out the dough and separate it into small portions. Flatten the dough and wrap up one portion of fillings (the lotus seed paste and salted egg yolk) in the center. Set aside.
4. Place the filled packet in the mold, gently pressing to fit into mooncake shape. Invert and remove the mold.
5. Put the mooncake into oven. Bake 5 minutes at 250degrees centigrade. Take out and brush the egg yolk on the surface of the mooncake. Put back into oven and bake 5 minutes more at 190 degrees centigrade until in golden brown. Let cool before serving.