Place all the ingredients in a large saucepan and heat gently, stirring until sugar dissolves. Bring to the boil, cover and boil for 3 minutes. Uncover and continue to boil until the temperature reaches 116 °C / 240 °F.
Remove from the heat and beat until the mixture becomes thick and creamy. Pour into a greased 8 inch tin.
Leave for 30 minutes. Mark into squares with a knife and leave until set. Cut into pieces and store in an airtight container.