Combine all the ingredients except the salt and Johnnie Walker in a saucepan and bring to a simmer, stirring to dissolve the sugar.
Simmer, stirring occasionally for about 10-15 minutes until the mixture reaches 114C.
Remove from the heat and stir through the Johnnie Walker and a pinch of salt.
Stand for 5 minutes, then beat the mixture with a spatula for about 10 minutes until it is no longer shiny and starting to firm.
Transfer to a 20 cm square baking tray roughly lined with baking paper.
Allow to cool either at room temperature or in the fridge, then cut into 2 cm squares.
Sprinkle with a little more sea salt and serve.