14 fl.oz/420 ml tin condensed milk

Place all the ingredients in a large pan and bring to the boil.

Reduce the heat

Simmer gently for 30 - 40 minutes, stirring occasionally.

As it starts to darken, stir continuously, ensuring it doesn't stick to the bottom of the pan

When it is a dark caramel colour remove from the heat and whisk hard (preferably with an electric whisk)

Keep whisking until the mixture cools and begins to thicken.

2 lb/1kg sugar

9 oz/270g butter

Pour mixture into a baking tray (around 9" x 12"). Leave to set for around 10 minutes. Cut into squares. Leave to harden and remove from the tray