Melt and temper the chocolate (see additional notes). Coat your egg moulds with a layer of melted chocolate; this is easiest to do by placing the chocolate into a piping bag, completely filling the moulds, and then turning then over and letting the excess drip out onto a sheet of baking paper. This gives you a thin, even coating.
Leave to set. You should have some chocolate left over which will be used to finish the eggs.
Meanwhile, make a sugar syrup by melting the sugar into the water.
Split the grated fondant into two bowls, 175 g in one and 25 g in the other. Colour the 25 g with yellow food colouring. Add a dribble of sugar syrup to make the correct gooey texture.
Add the vanilla and remaining sugar syrup to the white icing and mix to the correct texture (it should be thick but gooey).
With a piping bag, nearly fill each half egg with the white fondant, then top with a dollop of yellow fondant to form the yolk, making sure you leave 2 mm at the top for the chocolate.
Re-temper the leftover chocolate and use it to top the filled eggs, covering the fondant, then leave to set. The chocolates will release from the mould after 30 minutes or so in the fridge.
If you would like whole egg shapes, attach two halves together with a tiny blob of melted chocolate and leave to set.