500ml condensed milk
125g white sugar
10g unsalted butter
Take a saucepan and place on a low heat. Add the condensed milk and 100g of the sugar, stirring constantly.
In a separate pan, heat the remaining 25g of sugar together with half the butter until golden brown and caramelized. Make sure to stir constantly, as this is what gives this sweet treat its colour.
Add the caramel to the condensed milk mixture and simmer for 20-25 minutes, or until it is bubbling and becomes stiff in texture.
Rub a chopping board or ridge-less baking tray with the remaining butter. Spread the thick toffee mixture on to the buttered board and pat down with cling film until around 1½ cm thick. You should end up with a relatively smooth finish. Leave to cool for around 10 minutes then cut into bite size pieces.