1. Melt together all ingredients in a large saucepan over a medium heat until butter is melted and sugar has dissolved.

2. Using a sugar thermometer, keep the saucepan on a medium heat and leave the syrup to hit hard crack or 146°C, this will take a good 40 minutes or more, if the thermometer sticks at a lower temperature for a while, don't worry it will move again eventually! The sugar will bubble up a fair bit in the pan, so it is advisable to use a deep saucepan. Try not to stir the syrup too much while you wait for it to hit the correct temperature at it will knock the temperature back each time.

3. While waiting for the syrup to reach temperature grease a square or rectangle cake pan with either butter or oil (I use a swiss roll tin size so it not too thick when poured). Once you have reached hard crack pour the mixture into the tin and leave to cool for at least an hour, then place in the fridge for at least another hour to set it firm.

4. Once set solid, take either a toffee hammer or a rolling pin and firmly hit the toffee to break it into chunks, it should lift out of the tin pretty easily once you've got that first bit out.