Melt 375g of the chocolate in a double boiler, stirring constantly. Using a sugar thermometer, bring the chocolate to 48 degrees C for plain chocolate or 45 degrees C for milk chocolate. Remove from heat.
To temper the chocolate, add in the remaining unmelted chocolate. Stir well, until smooth. When the chocolate reaches 32 degrees C for plain chocolate or 30 degrees C for milk chocolate, it's ready to use.
Whilst waiting for the chocolate to cool, melt the white chocolate in the double boiler. (You don't need to worry about tempering the white chocolate, however.)
Drizzle the melted white chocolate in the egg moulds using a spoon. (The effect is up to you - make a criss-cross pattern, or drizzle either only horizontally or vertically. Get creative!) Place the moulds in the fridge to chill for 5 minutes.
Drizzle the melted plain or milk chocolate over the white chocolate, then use a pastry brush to brush over the entire surface of the mould till covered. Chill for 10 minutes in the fridge. Brush again with chocolate, then chill again for 10 minutes. Finally, brush a third time and chill for a final 10 minutes.
Carefully unmould the egg halves and trim the edges with a sharp knife. Brush the edges with a little melted chocolate, then carefully bring two halves together to form a single egg. Carefully set back in the mould and chill for 10 to 15 minutes, or until set.