Lightly oil a baking tray with groundnut oil.
Put the sugar, butter, cream of tartar and 75ml/2½fl oz water into a heavy-bottomed pan. Heat the mixture on a moderate heat, stirring all the time until the sugar has dissolved. Place a sugar thermometer in the pan, bring the mixture to the boil and bubble until the temperature reaches 137C/280F. (CAUTION: boiling sugar is extremely hot. Handle very carefully. Use a deep pan to avoid bubbling over.)
Quickly pour the mixture onto the prepared baking tray, taking care as the mixture is very hot.
Leave for about 20 minutes until cool enough to handle.
Put on rubber gloves and oil them with groundnut oil.
Take two diagonally opposite corners of the toffee and pull them over into the middle of the toffee. Then take the other two opposite corners and pull them into the middle to almost meet the others. Take two corners and stretch the toffee out like a long sausage, then take the ends and fold them into the middle. Take hold of the two ‘new’ ends and pull them out like a sausage again, fold them into the centre and keep repeating. Keep doing this about 10 or 15 times. The toffee will turn into spaghetti-type strands. Now twist the strands together like a corkscrew to form tight barley twist ringlets. Chop into 2.5cm/1in long sticks using some sturdy scissors.
Wrap in individual parchment twist wraps or pretty cellophane. The toffee will keep for a long time so long as it is wrapped and kept dry.