In a reasonably large pan with a thick bottom, pour the evaporated milk, sugar and butter. (Tip: cut your butter into small cubes so it melts quicker.)
Heat the mixture on medium heat and stir constantly until the sugar has dissolved and the butter has melted.
When it bubbles and is boiling, cook at exactly that heat for around 20 minutes. Make sure to keep stirring.
When the mixture is quite thick and a glossy, golden brown colour, turn off the heat. If the mixture starts to look brown in some places, take it off the heat immediately and stir vigorously till the brown bits are gone.
Cool for 5 minutes.
Then beat it with an electric mixer until it loses some of its gloss and becomes thicker. This should take 5-10 minutes.
Then, add your vanilla essence. Whisk again so it is no longer visible and pour into a tin lined with tin foil or grease proof paper.
Leave to cool for 2-3 hours, and then slice into cubes and enjoy!