Measure out all ingredients and place in a heavy bottomed non-stick saucepan
Bring the mixture to a lively simmer in the saucepan over medium heat, continually stirring to prevent it from catching. Stand well back from pot as mixture can get very hot and it can spit.
Using a sugar thermometer or digital equivalent, continue to stir mixture until it reaches 115°C, the soft ball stage method can be used if you have no thermometer.
Once at the correct temperature, remove from the heat and add the espresso and stir. Leave to cool briefly for a few minutes
Once cooled a little, beat vigorously with an electric hand mixer for around 5 minutes until the mixture is thickened and is no longer shining and has a matte finish
Place mixture in a greaseproof lined tin and even out with an offset spatula (I used a 9-inch square cake tin). Place in fridge for 3 hours before cutting into individual square servings.