In a heavy based pan over a low heat, dissolve the sugar in the water (do not stir).
When fully dissolved, add the remaining ingredients, turn up the heat and bring to the boil (again, do not stir) to 140C (use a sugar thermometer). This will take 20-35 mins.
As soon as it reaches temperature, pour the toffee into the prepared tin and leave to cool.
Once cold remove from tin and break with a toffee hammer.
Recipe by appetite magazine at https://www.appetitemag.co.uk/treacle-toffee/