Place all the ingredients in a heavy-based saucepan. Stir over a low heat until dissolved. Bring to the boil and boil gently for about 1 0 minutes until a little of the mixture, dropped into a cup of cold water, forms a soft ball when rolled between finger and thumb. Remove from the heat, stand the pan on a cool surface for 5 minutes, then beat until thick and beginning to grain.

Pour into a buttered 20.5 x 15 cm (8 x 6 inch) tin, mark into squares and cut when cold.