1. Gently heat the sugar, butter, vinegar, water and syrup in a heavy-based saucepan until the sugar has dissolved and the butter has melted.
2. Boil rapidly for 5 minutes until a drop of the mixture placed in cold water separates into threads which become hard but not brittle.
3. Wash and dry the apples and impale on the sticks.
4. Dip each one into the toffee mixture, swirling it around, so that the excess toffee drips back into the saucepan.
5. Leave to cool on a buttered baking sheet.