Photograph: Martin Poole
Heat the sugar, syrup and vinegar with 2 tablespoons of water in a heavy-based pan, gently swirling the pan until the sugar has dissolved.
Increase the heat and boil for 5-6 minutes, until the syrup reaches the ‘hard crack' stage, at 150°C (see below). Remove from the heat and stir in the butter.
Swiftly dip each apple in the toffee, tilting the pan to create a deep pool of toffee and swirling the apples to get an even coating. Allow the excess to drip off each apple into the pan for a moment, then set them, fork up, on a lightly oiled plate and leave to harden.
For a delicious variation, stir 2 tablespoons orange extract and 2 tablespoons sesame seeds into the toffee with the butter.
Get ahead: the toffee apples will keep for a few hours somewhere cool and dry, any longer and they start to 'weep'.
Kitchen secret: use forks instead of lollipop sticks to skewer your toffee apples for a quirky presentation. If you don’t have a sugar thermometer, drip a little toffee from a spoon into a dish of cold water. If it hardens to brittle threads immediately, it’s ready; if it’s still soft, the toffee needs a little more cooking time.