1. Heat the sugar and milk in a heavy based saucepan until the sugar dissolves.
2. Add the syrup and butter and bring to the boil.
3. Continue to boil for 2-3 minutes and then stir in the condensed milk.
4. Bring back to the boil and continue boiling until a drop of the mixture placed in cold water forms a soft ball when rolled in the fingers.
5. Remove from the heat, beat until thick and creamy and pour into a buttered shallow square tin.
6. Mark into squares, leave to set, then cut into the squares.