Like candied citrus slices, you can also use any type of citrus fruit for this.
Wash the fruits. Cut them in half and juice them. Place the juiced shells in a pan and cover with cold water. Bring to the boil and cook for 10 minutes.
Drain, then return them to the pan and cover with fresh water. Bring to the boil again and drain. Repeat the blanching process until no resistance is felt when the peel is pierced with a knife.
Drain and allow to cool. Scrape away the pith using a spoon. Slice the peel into 1cm/½ in strips with a sharp paring knife.
Place 800g/1¾lb/4 cups granulated (white) sugar in a clean pan with 400ml/14fl oz/1⅔ cups water. Stir over medium heat to dissolve the sugar.
Add the peel and bring to the boil. Boil for 45 minutes, until the syrup reduces and small bubbles form on top. Leave the peel to cool in the syrup overnight.
Transfer the peel to a wire rack placed over a piece of baking parchment to catch the drips. Leave to dry for 24 hours, then toss in caster (superfine) sugar.