Push a metal skewer into the top pointed end of each egg to make a hole, then pick away some of the shell until the hole is 1 cm (½ inch) in diameter. Tip out the contents of the egg into a bowl (you can use this for another recipe). Rinse the shell under cold running water then upturn to dry for 20 minutes, or 'blow dry' inside the eggs on a low setting of a hair dryer.
Melt the white and milk chocolate in separate bowls over pans of simmering water (see
Pipe or spoon the dulce de leche (toffee caramel) into each egg. Fill each egg with half the melted milk chocolate and chill for 2 hours until the chocolate is really firm.
Tap the egg shell gently to crack it and carefully peel away the shell, trying not to finger the chocolate too much. Place each egg in an egg cup. To eat your egg, run a knife under hot water, dry it, then slice the chocolate with the warm knife.