Cut four large oranges into quarters and remove the flesh. If the peel is very pithy the cut away some of the white pith but to not make the peel too thin.
Cut the peel into 6-10 mm (¼-½in) wide strips. Place the peel strips in a saucepan and cover with water. Bring quickly to the boil then reduce the heat and simmer 10 minutes.
Drain and refill the pan with water to cover the peel again. Bring to the boil and simmer for 10 minutes, drain then repeat this step once more time. Drain and set the peel aside.
Place 750g (1lb 6oz) sugar in a saucepan with 600ml (1 pt) water. Heat stirring, until the sugar is dissolved, then bring to the boil and simmer for 10 minutes.
Add the orange peel and bring back to a simmer. Then simmer for 50-60 minutes or until the pith is semi-translucent. Remove from the heat then transfer the peel with a slotted spoon and spread out on a wire rack set over a baking tray to catch the drips .
Allow to dry for at least 12 hours or up to 36 hours in a cool dry space - Do not refrigerate.
Break about 100g (3½oz) of the plain chocolate into squares and place in a heatproof bowl set over a pan of hot water until melted. remove from the heat. Chop 50g (2oz) chocolate into small pieces and stir in the melted chocolate, continue to stir until all the chocolate has melted.
Dip each piece of orange peel into the chocolate allowing the excess to run back into the bowl then place on a baking sheet lined with baking parchment. Allow the chocolate to set in a cool dry place before serving.
For plain candied peel, toss the peel after drying in caster sugar to coat.