Put all ingredients, apart from vanilla essence, in a pot and bring to the boil stirring all the time.
Boil for roughly 20 minutes, still stirring all the time.
In a bowl of cold water drop a little of the fudge mixture (test throughout the 20 mins of boiling), when it is at the soft ball stage remove from heat.
Add vanilla essence and beat with an electric beater for approximately 5 minutes until you can see it starting to set.
Pour into greased tin (or lined with baking paper) and place in fridge to cool and set.
Cut into pieces once set and keep in the fridge or locked pantry to avoid eating it all at once!